JPH1196585A - Recording/reproducing method of optical information recording medium, optical pickup device, condenser optical system, objective lens and method for designing objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce plural optical disks with one condenser optical system, to embody the reproduction at a low cost without complication and to deal with the optical disk of high NA as well. SOLUTION: The refraction surface S1 on the light source side of the objective lens 16 of the optical pickup device is provided with three splitting surfaces Sd1 to Sd3. The luminous fluxes passing the first splitting surface Sd1 and the third splitting surface Sd3 are utilized at the time of reproducing the first optical disk of t1 in the thickness of a transparent substrate and the luminous fluxes passing the first splitting surface Sd1 and the second splitting surface Sd2 are utilized at the time of reproducing the second optical disk of t2 (t2≠t1) in the thickness of the transparent substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam emitted from a light source, which is condensed on an information recording surface by a condensing optical system, and records information on an optical information recording medium to be reproduced or reproduces information on the information recording surface. The present invention relates to a recording / reproducing method for an optical information recording medium, an optical pickup device, a condensing optical system, an objective lens, and a method for designing an objective lens used for these.

[0002]

2. Description of the Related Art In recent years, with the practical use of a short-wavelength red semiconductor laser, a high-density optical disk having the same size and large capacity as a CD (compact disk), which is a conventional optical information recording medium (also referred to as an optical disk), has been developed. The development of DVDs (also referred to as digital video discs or digital versatite discs) as optical information recording media has been progressing. This D
In VD, the numerical aperture NA of the objective lens on the optical disk side when using a short-wavelength semiconductor laser of 635 nm is 0.6.
And DVD has a track pitch of 0.74.
μm, the shortest pit length is 0.4 μm, and the density is reduced to less than half of the CD track pitch of 1.6 μm and the shortest pit length of 0.83 μm. Also, the CD mentioned above,
In addition to DVD, optical disks of various standards, for example, CD
-R (write-once compact disc), LD (laser disc), MD (mini disc), MO (magneto-optical disc), and the like have also been commercialized and spread. Table 1 shows the thicknesses of the transparent substrates of the various optical disks and the required numerical apertures.

[0003]

[Table 1]

[0004] For CD-R, the light source wavelength λ = 7
It must be 80 (nm), but in other optical discs, a light source having a wavelength other than the light source wavelength described in Table 1 can be used. In this case, the required numerical aperture depends on the used light source wavelength λ. NA changes. For example, in the case of a CD, the required numerical aperture is approximated by NA = λ (μm) /1.73, and in the case of a DVD, the required numerical aperture is approximated by NA = λ (μm) /1.06.

The numerical aperture (for example, hereinafter referred to as NA1, NA2, NAL, NAH, NA3, NA4, etc.) referred to in the present specification is the numerical aperture of the condensing optical system viewed from the transparent substrate side. It is.

As described above, the market is now in the age of various optical disks having different sizes, substrate thicknesses, recording densities, wavelengths to be used, etc., and optical pickup devices capable of supporting various optical disks have been proposed. .

As one of them, there has been proposed an optical pickup device having a focusing optical system corresponding to each of different optical disks and switching the focusing optical system depending on the optical disk to be reproduced. However, in this optical pickup device, a plurality of condensing optical systems are required, which not only causes an increase in cost, but also requires a drive mechanism for switching the condensing optical systems, complicates the device, and requires a switching accuracy thereof,
Not preferred.

Therefore, various optical pickup devices for reproducing a plurality of optical disks by using one condensing optical system have been proposed.

One of them is disclosed in Japanese Patent Application Laid-Open No. 7-302439.
Japanese Patent Application Laid-Open Publication No. H11-176,086 describes an optical pickup device that divides a refraction surface of an objective lens into a plurality of ring-shaped regions, and reproduces the image by forming a beam on one of optical disks having different thicknesses. ing.

[0010] In addition, JP-A-7-57271 discloses that
In the case of the first optical disc having the transparent substrate thickness t1, an objective lens designed so that the wavefront aberration of the focused beam is 0.07λ or less is used, and the transparent substrate thickness t2 is used.
In the case of the second optical disc, an optical pickup device that forms a condensed spot in a slightly defocused state is described.

[0011]

However, in the optical pickup device described in Japanese Patent Application Laid-Open No. 7-302439, since the amount of incident light is simultaneously divided into two focal points by one objective lens, the laser output is increased. Required, resulting in high costs. Also, Japanese Patent Application Laid-Open No. 7-57271
In the optical pickup device described in Japanese Patent Application Laid-Open No. H10-207, jitter increases due to side lobes during reproduction of the second optical disk. In particular, the wavefront aberration of the first optical disc is 0.07
Since the second optical disc is forcibly reproduced by the objective lens having a value of λ or less, the reproducible numerical aperture of the second optical disc is limited.

Therefore, the present invention can record or reproduce a plurality of optical information recording media with one condensing optical system, can be realized at low cost and without complication, and can be applied to a high NA optical information recording medium. The purpose is to be able to do it.

Further, the present applicant has filed Japanese Patent Application No. 8-156683.
And Japanese Patent Application No. 8-180586,
It is an object of the present invention to further improve the light-collecting characteristics of an optical pickup device in which spherical aberration is adjusted.

[0014]

The above object can be attained by the following constitution.

(1) The first optical information recording medium having a transparent substrate having a thickness of t1 and the transparent substrate having a thickness of t2 (where t2 ≠ t
With respect to the second optical information recording medium of 1), the light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system, and the information is recorded or recorded on the information recording surface. In a recording / reproducing method for an optical information recording medium for reproducing information on a recording surface, a first light flux near an optical axis is used for recording or reproducing on a first optical information recording medium and recording or reproducing on a second optical information recording medium. At the same time, the second light beam outside the first light beam is mainly used for recording or reproduction of the second optical information recording medium, and the third light beam outside the second light beam is mainly used for the first optical information recording medium. A recording / reproducing method for an optical information recording medium, which is used for recording or reproduction.

(2) The first optical information recording medium having a transparent substrate having a thickness of t1 and the transparent substrate having a thickness of t2 (where t2 ≠ t
With respect to the second optical information recording medium of 1), the light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system, and the information is recorded or recorded on the information recording surface. In an optical pickup device for reproducing information on a recording surface, the condensing optical system uses the first light flux near the optical axis for recording or reproducing on the first optical information recording medium and recording or reproducing on the second optical information recording medium. The second light beam outside the first light beam is mainly used for reproducing the second optical information recording medium, and the third light beam outside the second light beam is mainly used for recording or reproducing on the first optical information recording medium. An optical pickup device having a function to be used for optical pickup.

(3) An optical pickup device for condensing a light beam from a light source on an information recording surface of an optical information recording medium and recording information on the information recording surface or reproducing information recorded on the information recording surface. , At least one optical surface constituting the condensing optical system is formed by sandwiching a second division surface between the first division surface located at the center of the optical surface near the optical axis and the first division surface. When recording or reproducing on the first optical information recording medium having a transparent substrate having a thickness of t1, the first divided surface and the third divided surface are mainly constituted by an optical surface divided into a third divided surface located thereon.
When a beam spot is formed by a light beam passing through the division surface and recording or reproduction is performed on the second optical information recording medium having a transparent substrate having a thickness of t2 (where t2 ≠ t1), the first division is mainly performed. An optical pickup device, wherein a beam spot is formed by a light beam having passed through a surface and a second division surface.

(4) At least one surface has a plurality of divided surfaces concentrically with the optical axis and a plurality of divided surfaces.
A first dividing surface near the optical axis and a third dividing surface outside the first dividing surface;
When the light flux passing through the division plane is measured so as to form an image at substantially the same first imaging position, the second division between the first imaging position and the first division plane and the third division plane is measured. The absolute value of the distance from the second imaging position where the light flux passing through the surface forms an image is 4
An objective lens having a size of not less than μm and not more than 40 μm.

(5) At least one surface has a plurality of divided surfaces concentrically with the optical axis and has a plurality of divided surfaces.
A first dividing surface near the optical axis and a third dividing surface outside the first dividing surface;
When the light beam passing through the division surface is measured so as to form an image at substantially the same first imaging position, the light beam passing through the second division surface between the first division surface and the third division surface forms an image. An objective lens wherein the second image forming position is closer to the objective lens than the first image forming position.

(6) The objective lens according to (5), wherein a distance between the first position and the second position is not less than −40 μm and not more than −4 μm.

(7) At least one surface has a plurality of divided surfaces concentrically divided with the optical axis,
When passing through a transparent substrate of a predetermined thickness with a predetermined incident light beam,
Of the luminous flux passing through the first division plane including the optical axis, the position where the light ray passing near the optical axis intersects the optical axis and the light ray passing through the end of the first division plane in a direction orthogonal to the optical axis are Between the position intersecting with the optical axis, the light beam passing through the second division surface outside the first division surface intersects the optical axis, and the light beam passing through the third division surface outside the second division surface is The position of a ray passing near the optical axis intersecting the optical axis,
An objective lens, wherein a light beam passing through an end portion of the division surface intersects the optical axis at a position farther than a position intersecting the optical axis.

Further, when viewed at a substantially central position of the second division surface in a direction perpendicular to the optical axis, an angle between a normal line of the second division surface and the optical axis, the first division surface, and The difference between the normal line of the plane interpolated from the third division plane outside the second division plane and the angle between the optical axis and the optical axis is in the range of 0.02 ° to 1 °. The objective lens (7-1) according to any one of 4) to (7) is preferable.

Further, when the light beams passing through the first divided surface near the optical axis and the third divided surface outside the second divided surface are measured so as to form an image at substantially the same image forming position, (4) to (7), (7-), wherein the best wavefront aberration due to the light beam passing through the first division surface and the third division surface is 0.05λrms or less (where λ is the wavelength of the light source).
Objective lens (7-2) according to any one of 1)
Is preferred.

Further, when a predetermined incident light beam passes through a transparent substrate having a predetermined thickness, the best wavefront aberration caused by the light beam passing through the first division surface is 0.07λrms or less (where λ
Is the wavelength of the light source).
The objective lens (7-3) according to any one of (7), (7-1), and (7-2) is preferable.

(8) The light beam emitted from the light source is condensed as a light spot on the information recording surface of the optical information recording medium through the transparent substrate of the optical information recording medium by the condensing optical system, and the information is recorded on the information recording surface. In the optical pickup device for recording the information or reproducing the information recorded on the information recording surface, the light condensing optical system necessary for recording or reproducing the first optical information recording medium having the transparent substrate having a thickness of t1 is provided. The required numerical aperture on the optical information recording medium side is NA1, and the thickness of the transparent substrate is t2 (where t2 ≠
When the required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the second optical information recording medium at t1) is NA2 (where NA2 <NA1), the light condensing is performed. An optical pickup device, wherein the optical system has a function of causing spherical aberration to change discontinuously at at least two aperture positions near NA2.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, when t2> t1, when viewed from the small numerical aperture to the large numerical aperture, The condensing optical system has a function of changing the spherical aberration discontinuously in a negative direction at a numerical aperture NAL, and having a function of changing the spherical aberration discontinuously in a positive direction at a numerical aperture NAH. The optical pickup device (8-1) described in (8) is preferable.

Further, when the light passes through the transparent substrate having a thickness of t2 (where t2> t1), the condensing optical system has a function of making the spherical aberration between the numerical apertures NAL and NAH positive. The optical pickup device (8-2) according to (8-1), wherein the optical pickup device has (8-1), is preferable.

Further, t1 = 0.6 mm, t2 = 1.2
mm, 610 nm <λ <670 nm, 0.32 <NA2
When <0.41, the condensing optical system is set to 0.60 (NA
2) <NAL <1.3 (NA2), and the optical pickup device (8-3) described in (8-1) or (8-2) is preferable.

Further, t1 = 0.6 mm, t2 = 1.2
mm, 610 nm <λ <670 nm, 0.32 <NA2
When <0.41, the condensing optical system is set to 0.01 <NA
H-NAL <0.12 (8-
The optical pickup device (8-4) according to any one of 1) to (8-3) is preferable.

Further, when the light passes through the transparent substrate having a thickness of t2, the condensing optical system changes the numerical aperture from NAL to NAH.
Is between -2λ / (NA2) ² or more and 5λ /
The optical pickup device (8-5) according to (8-3) or (8-4), wherein (NA2) is ² or less, is preferable.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the condensing optical system is arranged such that when the light passes through a transparent substrate having a thickness of t1, When the numerical aperture on the optical information recording medium side of the condensing optical system is NA1, the best wavefront aberration excluding the range from the numerical aperture NAL to the numerical aperture NAH is 0.05λrms or less (where λ is the wavelength of the light source). The optical pickup device (8-6) according to any one of (8) and (8-1) to (8-5), which is characterized in that:

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the condensing optical system is arranged such that when the light passes through a transparent substrate having a thickness of t2, (8), (8-1) to (8-6), wherein the best wavefront aberration up to the numerical aperture NAL is 0.07λrms or less (where λ is the wavelength of the light source).
Optical pickup device according to any one of (8-7)
Is preferred.

Further, the light source comprises a first light source having a wavelength λ1 for recording or reproducing information on or from a first optical information recording medium;
Any one of (8), (8-1), and (8-2), including a second light source having a wavelength λ2 (where λ2> λ1) for recording or reproducing information on or from the optical information recording medium. The optical pickup device (8-8) described above is preferable.

Further, among the at least two opening positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, t1 = 0.6 mm, t2 = 1.2 mm, 6
10 nm <λ1 <670 nm, 740 nm <λ2 <87
When 0 nm and 0.40 <NA2 <0.51, the condensing optical system operates as follows: 0.60 (NA2) <NAL <1.1 (NA
The optical pickup device (8-9) according to (8-8), which is characterized by (2), is preferable.

Further, among the at least two opening positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, t1 = 0.6 mm, t2 = 1.2 mm, 6
10 nm <λ1 <670 nm, 740 nm <λ2 <87
When 0 nm and 0.40 <NA2 <0.51, the converging optical system satisfies 0.01 <NAH-NAL <0.12 (8-8) or (8-9) The optical pickup device (8-10) described in (1) is preferable.

Further, when the light passes through the transparent substrate having a thickness of t2, the condensing optical system changes the numerical aperture from NAL to NAH.
Is greater than or equal to -2 (λ2) / (NA2) ² ,
The optical pickup device (8-11) according to any one of (8-9) and (8-10), wherein the ratio is not more than 5 (λ2) / (NA2) ² , is preferable.

Further, the paraxial imaging magnification of the objective lens having a positive refractive power as the condensing optical system with respect to the first light source and the imaging magnification with respect to the second light source are substantially zero.
(8-8) to (8-1)
The optical pickup device according to any one of (1) to (8-).
12) is preferred.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the condensing optical system is arranged such that when the light passes through a transparent substrate having a thickness of t1, When the numerical aperture on the optical information recording medium side of the condensing optical system is NA1, the best wavefront aberration excluding the range from the numerical aperture NAL to the numerical aperture NAH is 0.05λ1 rms.
The optical pickup device (8-13) according to any one of (8-8) to (8-12) is characterized in that it has the following function (where λ1 is the wavelength of the first light source). preferable.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the condensing optical system is arranged such that when the light passes through a transparent substrate having a thickness of t2, (8-8) to (8-1), wherein the best wavefront aberration up to the numerical aperture NAL is 0.07λ2 rms or less (where λ2 is the wavelength of the second light source).
The optical pickup device according to any one of 3) (8-
14) is preferred.

Further, the condensing optical system has an objective lens having a positive refractive power (8), (8-).
The optical pickup device (8-15) according to any one of 1) to (8-14) is preferable.

(9) The light flux from the light source is condensed as a light spot on the information recording surface of the optical information recording medium via the transparent substrate of the optical information recording medium, and information is recorded on the optical information recording medium or In an objective lens of a pickup device for reproducing information recorded on an information recording medium, the objective necessary for recording or reproducing the first optical information recording medium having a wavelength of a light source of λ and a thickness of a transparent substrate of t1. The required numerical aperture of the lens on the optical information recording medium side is NA1, and the thickness of the transparent substrate is t.
The required numerical aperture on the optical information recording medium side of the objective lens required for recording or reproducing the second optical information recording medium of 2 (where t2 ≠ t1) is NA2 (where NA2 <NA).
1), the numerical aperture is at least 2 near NA2.
An objective lens for an optical pickup device, wherein spherical aberration changes discontinuously at two aperture positions.

(10) When the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the numerical aperture NA in a direction orthogonal to the optical axis is
When viewed at approximately the center between L and the numerical aperture NAH, the numerical aperture N
The angle between the normal of the surface from AL to the numerical aperture NAH and the optical axis is the surface from the optical axis to the numerical aperture NAL and the numerical aperture NAH
Is larger when t2> t1 than the angle between the optical axis and the normal line of the surface interpolated from the surface up to the numerical aperture NA1 and t2
The objective lens of the optical pickup device according to (9), wherein the objective lens is small when <t1.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the numerical aperture NAL is perpendicular to the optical axis.
And the numerical aperture NAH when viewed at the approximate center of the numerical aperture NAH
The angle between the normal to the surface from L to the numerical aperture NAH and the optical axis, the normal to the surface from the optical axis to the numerical aperture NAL, and the normal to the surface interpolated from the surface from the numerical aperture NAH to the numerical aperture NA1 The objective lens (10-1) of the optical pickup device according to (9) or (10), wherein the difference from the angle with the axis is in the range of 0.02 ° to 1 °. .

Further, among the at least two opening positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, and when t2> t1, when viewed from the small numerical aperture to the large numerical aperture, the numerical aperture is In the NAL, the spherical aberration changes discontinuously in the negative direction, and in the numerical aperture NAH, the spherical aberration changes discontinuously in the positive direction. (9), (10), (10-1) The objective lens (10-2) of the optical pickup device described in any one of (1) and (2) is preferable.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, when a transparent substrate having a thickness of t2 (where t2> t1) is interposed, , From the numerical aperture NAL to the numerical aperture NA
Wherein the spherical aberration during H is positive (9),
(10) The objective lens (10-3) of the optical pickup device according to any one of (10-1) and (10-2) is preferable.

Further, among the at least two aperture positions, the smallest numerical aperture is NAL and the largest numerical aperture is NAH, and t1 = 0.6 mm, t2 = 1.2 mm, 6
10 nm <λ <670 nm, 0.32 <NA2 <0.4
At the time of 1, 0.60 (NA2) <NAL <1.3 (NA
(9), (10), (10)
The objective lens (10-4) of the optical pickup device according to any one of (1) to (10-3) is preferable.

Further, among the at least two opening positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, t1 = 0.6 mm, t2 = 1.2 mm, 6
10 nm <λ <670 nm, 0.32 <NA2 <0.4
At the time of 1, 0.01 <NAH-NAL <0.12, (9), (10), (10-1) to
The objective lens (10-5) of the optical pickup device according to any one of (10-4) is preferable.

Further, when the light passes through the transparent substrate having a thickness of t2, the spherical aberration between the numerical aperture NAL and the numerical aperture NAH becomes
The objective lens (10-6) of the optical pickup device described in (10-4) or (10-5), which is not less than -2λ / (NA2) ^{2 and not} more than 5λ / (NA2) ² , is preferable. .

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the optical information of the objective lens passes through the transparent substrate having a thickness of t1. The numerical aperture on the recording medium side is NA
1, wherein the best wavefront aberration excluding the range between the numerical aperture NAL and the numerical aperture NAH has a function of 0.05 λrms or less (where λ is the wavelength of the light source) (9), (10) ), The objective lens (1) of the optical pickup device according to any one of (10-1) to (10-6).
0-7) is preferred.

Further, when the smallest numerical aperture is NAL and the largest numerical aperture is NAH among the at least two aperture positions, the best numerical aperture up to the numerical aperture NAL can be obtained through a transparent substrate having a thickness of t2. Wavefront aberration is 0.07λrm
s or less (where λ is the wavelength of the light source), the objective of the optical pickup device according to any one of (9), (10), (10-1) to (10-7). A lens (10-8) is preferred.

Further, among the at least two aperture positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, the wavelength of the light source for recording or reproducing on the first optical information recording medium is λ1, the second is The wavelength of the light source for recording or reproducing on the optical information recording medium is λ2 (where λ2> λ
1), t1 = 0.6 mm, t2 = 1.2 mm, 61
0 nm <λ1 <670 nm, 740 nm <λ2 <870
nm, 0.40 <NA2 <0.51, 0.60
(9), (10), (10-1) to (10-), wherein (NA2) <NAL <1.1 (NA2).
The objective lens (10-9) of the optical pickup device according to any one of 3) is preferable.

Further, of the at least two aperture positions, the smallest numerical aperture is NAL, the largest numerical aperture is NAH, the wavelength of the light source for recording or reproducing on the first optical information recording medium is λ1, the second is The wavelength of the light source for recording or reproducing on the optical information recording medium is λ2 (where λ2> λ
1), t1 = 0.6 mm, t2 = 1.2 mm, 61
0 nm <λ1 <670 nm, 740 nm <λ2 <870
nm, when 0.40 <NA2 <0.51, 0.01 <
NAH-NAL <0.12, (9), (10), (10-1) to (10-3), (1)
The objective lens (10-10) of the optical pickup device according to any one of 0-9) is preferable.

Further, when the light passes through the transparent substrate having a thickness of t2, the condensing optical system changes the numerical aperture from NAL to NAH.
Is greater than or equal to -2 (λ2) / (NA2) ² ,
The objective lens (10-11) of the optical pickup device described in (10-9) or (10-10), which has a function of not more than 5 (λ2) / (NA2) ^2, is preferable.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the wavelength of the light source for recording or reproducing on the first optical information recording medium is λ1, The wavelength of the light source for recording or reproducing the second optical information recording medium is λ2 (where λ2
> Λ1), and the best wavefront excluding the numerical aperture NAL and the numerical aperture NAH among the numerical aperture NA1 on the optical information recording medium side of the objective lens when passing through the transparent substrate having a thickness of t1. (9) characterized in that it has a function of having an aberration of 0.05λrms or less (where λ is the wavelength of the light source).
(10), (10-1) to (10-3), (10-9)
The objective lens (10-12) of the optical pickup device according to any one of (1) to (10-11) is preferable.

Further, when the smallest numerical aperture among the at least two aperture positions is NAL and the largest numerical aperture is NAH, the wavelength of the light source for recording or reproducing on the first optical information recording medium is λ1, The wavelength of the light source for recording or reproducing the second optical information recording medium is λ2 (where λ2
> Λ1), and the best wavefront aberration up to the numerical aperture NAL is 0.07λrms or less (where λ is the wavelength of the light source) when passing through a transparent substrate having a thickness of t2 (9). , (10), (10-1) to (10-3), (1
The objective lens (10-13) of the optical pickup device according to any one of (0-9) to (10-12) is preferable.

(11) In a method for designing an objective lens for condensing a light beam emitted from a light source having a wavelength λ on a plurality of optical information recording media having different thicknesses of a transparent substrate, the first substrate having a thickness t1 of the transparent substrate may be used. Within the range of the numerical aperture NA1 on the optical information recording medium side of the objective lens required for recording or reproduction of the optical information recording medium, the light flux condensed on the first optical information recording medium via the transparent substrate having a thickness t1. Best wavefront aberration is 0.05λrm
The first aspherical surface and the common refraction surface are designed to be equal to or less than s, and the thickness of the transparent substrate is t2 (where t2 ≠ t
The amount of spherical aberration of the light beam focused on the second optical information recording medium in 1) is larger than the amount of spherical aberration generated when the light beam is focused on the second optical information recording medium via the first aspheric surface. A second aspherical surface with respect to the common refraction surface is designed so as to reduce the number, and the first aspherical surface and the second aspherical surface are used to record information of an objective lens necessary for recording or reproducing of the second optical information recording medium. When the numerical aperture on the surface side is NA2 (where NA2 <NA1), the first aspherical surface is combined so that the second aspherical surface is located at a portion through which the light flux near the NA2 passes. A method for designing an objective lens, comprising designing at least one refractive surface of the objective lens.

(12) The method for designing an objective lens according to (11), wherein an on-axis radius of curvature of the first aspheric surface and an on-axis radius of curvature of the second aspheric surface are the same.

(13) The first aspherical surface passes through the first aspherical surface located on the optical axis side of the second aspherical surface to be synthesized,
(11) or (12), wherein the transparent substrate is designed such that the best wavefront aberration of the light beam focused on the second optical information recording medium having a thickness of t2 is 0.07λrms or less. How to design an objective lens.

(14) In an objective lens for condensing a light beam emitted from a light source on a plurality of optical information recording media having different thicknesses of the transparent substrate, at least one refraction surface of the objective lens is formed to have a thickness equal to the thickness of the transparent substrate. Is the best wavefront of the light beam condensed through the transparent substrate having the thickness t1 within the range of the numerical aperture NA1 on the optical information recording medium side of the objective lens required for recording or reproduction of the first optical information recording medium at t1. Aberration is 0.05λ
rms or less, and the amount of spherical aberration of the light beam focused on the second optical information recording medium having a thickness of the transparent substrate of t2 (where t2 ≠ t1) is the second light A second aspherical surface which is smaller than the amount of spherical aberration generated when the light is focused on the information recording medium via the first aspherical surface,
The numerical aperture on the information recording surface side of the objective lens required for recording or reproduction of the second optical information recording medium is NA2 (where NA2
An objective lens comprising: a refracting surface synthesized such that the second aspheric surface is located at a portion of the first aspheric surface where the light flux near the NA2 passes when <NA1).

(15) The light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by the condensing optical system on the first optical information recording medium having the transparent substrate having a thickness of t1, and the information recording is performed. In an optical pickup device for recording information on a surface or reproducing information on an information recording surface, the optical information recording medium side of the condensing optical system necessary for recording or reproducing the first optical information recording medium is required. The numerical aperture is NA1, and the thickness t of the transparent substrate is different from the thickness t1 of the transparent substrate of the first optical information recording medium.
Assuming that the necessary numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the second optical information recording medium having 2 (t2 ≠ t1) is NA2 (where NA2 <NA1), 0.60 (NA2) <NA
3 <1.3 (NA2) (However, the wavelength of the light source when recording or reproducing the second optical information recording medium is 740 nm to 870.
In the case of nm, the upper limit of this equation is 1.1 (NA2)), and the numerical aperture NA3 on the optical information recording medium side of the condensing optical system that satisfies the condition of 0.01 <NA4-NA3 <0.12.
Acting on the light beam passing between the first optical information recording medium and the numerical aperture NA4 to provide a surface for mainly utilizing the light beam for recording or reproduction of the second optical information recording medium, so that the thicknesses of the transparent substrates are different from each other. An optical pickup device, wherein recording or reproduction is performed on a first optical information recording medium and a second optical information recording medium by the same condensing optical system.

(16) The second image forming position of the second light beam passing through the surface mainly used for recording or reproduction of the second optical information recording medium is the first image position inside the second light beam. When the light beam and the third light beam outside the second light beam are measured so as to form an image at substantially the same first image forming position, the absolute value of the distance between the first image forming position and the first image forming position is 4 μm or more. The optical pickup device according to (15), wherein the optical pickup device has a thickness of 40 μm or less.

The optical pickup device (16-1) according to (15) or (16), further comprising a plurality of surfaces mainly used for recording or reproduction of the second optical information recording medium. Is preferred.

Further, when recording or reproducing the second optical information recording medium, the best wavefront aberration due to the light beam passing through a surface inside the surface mainly used for recording or reproduction of the second optical information recording medium. Is not more than 0.07λ rms (where λ is the wavelength of the light source) (15), (1)
The optical pickup device (16-2) according to any one of (6) and (16-1) is preferable.

(17) The first optical information recording medium having a transparent substrate thickness of t1 and the transparent substrate having a thickness of t2 (where t2 ≠
The light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system with respect to the second optical information recording medium of t1), and the information is recorded on the information recording surface or the information is recorded on the information recording surface. In an optical pickup device for recording / reproducing an optical information recording medium for reproducing information on a recording surface, the optical condensing optical system necessary for recording / reproducing the first optical information recording medium is provided on the optical information recording medium side. The required numerical aperture is NA1, and the required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the second optical information recording medium is NA2 (where NA2 <N
A1), when the condensing optical system is configured to obtain the best wavefront aberration within a range of the numerical aperture NA1 through a transparent substrate having a thickness t1 at a predetermined magnification, An optical pickup device characterized in that the wavefront aberration is discontinuous in at least two places near the numerical aperture NA2 when viewed from the aberration and the wavefront aberration curve with the numerical aperture on the horizontal axis.

Further, the vicinity of the numerical aperture NA2 is 0.1 mm.
60 (NA2) <NA3 <1.3 (However, the wavelength of the light source when recording or reproducing the second optical information recording medium is 740n
For m to 870 nm, the upper limit of this equation is 1.1 (N
A2)) (NA2), 0.01 <NA4-NA3
The optical pickup device (17-1) according to (17), which is between two numerical apertures NA3 and NA4 satisfying <0.12, is preferable.

Further, when recording or reproducing the second optical information recording medium, the condensing optical system passes through the optical axis side of the numerical aperture closest to the optical axis among the two places where the wavefront aberration is discontinuous. Characterized in that the best wavefront aberration due to the obtained light beam is 0.07 λrms or less (where λ is the wavelength of the light source).
7) or the optical pickup device (1) according to (17-1).
7-2) is preferred.

(18) The first optical information recording medium in which the thickness of the transparent substrate is t1 and the thickness of the transparent substrate are t2 (where t2 ≠
The light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system with respect to the second optical information recording medium of t1), and the information is recorded on the information recording surface or the information is recorded on the information recording surface. In an objective lens of an optical pickup device for recording / reproducing an optical information recording medium for reproducing information on a recording surface, at least one surface of the objective lens is 2n + 1 in order from a first division surface near an optical axis (wherein , N is a natural number), and the first light flux passing through the first division surface is used for recording or reproduction on the first optical information recording medium and recording or reproduction on the second optical information recording medium. At the same time, the light beam passing through the even-numbered division surface is mainly used for recording or reproduction on the second optical information recording medium, and the light beam passing through the odd-numbered division surface excluding the first division surface is mainly used for recording on the first optical information recording medium. Or used for reproduction The objective lens of the pick-up device.

Further, the numerical aperture on the optical information recording medium side on the optical axis side of the second division surface is set to NAL, and the optical information recording on the side of the second n-th division surface (where n is an integer greater than 2) remote from the optical axis. If the numerical aperture on the medium side is NAH, 0.8 (NA
2) <NAL <1.3 (NA2) (However, the wavelength of the light source when recording or reproducing the second optical information recording medium is 740 n
For m to 870 nm, the upper limit of this equation is 1.1 (N
A2)), 0.01 <NAH-NAL <0.12
It is preferable that the objective lens (18-1) of the optical pickup device described in (18) is satisfied.

Further, it has a function that the best wavefront aberration due to the light beam passing through the odd division plane is 0.05λrms or less (where λ is the wavelength of the light source) when passing through the transparent substrate having a thickness of t1. (18) or (18-
The objective lens (18-) of the optical pickup device described in 1).
2) is preferred.

Further, the best wavefront aberration due to the light beam passing through the first division surface when passing through the transparent substrate having a thickness of t2 is 0.07λrms or less (where λ is the wavelength of the light source). (18), (18-1), (18-
The objective lens (18-3) of the optical pickup device according to any one of 2) is preferable.

(19) A light beam of wavelength λ having a uniform phase from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, and information is recorded on the information recording surface. Alternatively, in an optical pickup device that reproduces information recorded on an information recording surface, a light beam from the light source is condensed by the condensing optical system via a parallel flat plate having a thickness of t1 and a refractive index of n1, and is converged. Within the range of the first numerical aperture on the plane plate side, the wavefront aberration curve obtained by measuring the wavefront aberration in a state where the wavefront aberration is the best is the first aperture on the parallel plane plate side of the condensing optical system. Within the range of the second numerical aperture smaller than the numerical value, there is a portion where the wavefront aberration is discontinuous, and the inclination of the wavefront aberration of the discontinuous portion is the portion of the discontinuous portion. Wavefront with a slope different from the slope of the straight line connecting the ends of the curves on both sides So that the difference curve, the optical pickup apparatus characterized by being configured of a plurality of divided surfaces at least one refractive surface of the light converging optical system in the optical axis concentrically.

The optical pickup device (19-1) according to (19), wherein there are a plurality of portions where the wavefront aberration is discontinuous within the range of the predetermined numerical aperture.
Is preferred.

Further, the predetermined numerical aperture is 0.60
(NA2) <NA3 <1.3 (NA2) (However, the second
The wavelength of the light source when recording or reproducing the optical information recording medium is 7
For 40 nm to 870 nm, the upper limit of this equation is 1.
1 (NA2)), 0.01 <NA4-NA3 <
The optical pickup device (19-2) according to (19) or (19-1), which is between NA3 and NA4 that satisfies 0.12.

Further, said t1 is 0.6 mm, and said n1 is 1.58 (19),
The optical pickup device (19-3) according to any one of (19-1) and (19-2) is preferable.

(20) In order to record information on the optical information recording medium or to reproduce the information recorded on the optical information recording medium, the light flux from the light source is placed on the information recording surface of the optical information recording medium. In an objective lens of an optical pickup device for condensing light as a light spot via a transparent substrate of a recording medium, a first optical information recording medium having a transparent substrate having a thickness of t1 and a transparent substrate having a thickness of t1 using a light source having a wavelength of λ1. t2 (however,
t2 ≠ t1), the light can be focused on the information recording surface of the second optical information recording medium, and the wavelength λ2 (where λ2
Even when a light source of (2 ≠ λ1) is used, light can be collected on the information recording surface of the second optical information recording medium.
An objective lens for an optical pickup device, wherein at least one surface of the objective lens is constituted by a plurality of divided surfaces.

(21) At least one surface has a plurality of divided surfaces concentrically divided into the optical axis and a plurality of divided surfaces, and the n-th divided surface (where n is an integer of 1 or more) is located on the optical axis side. The light transmitted through the (2n-1) division surface and the light transmitted through the (2n + 1) division surface opposite to the optical axis side from the 2n division surface are transmitted through the transparent substrate having a predetermined thickness. When they are made to have substantially the same phase, the light transmitted through the (2n-1) -th divided surface and the second n-th light in the direction orthogonal to the optical axis
The phase difference between the light transmitted through the second n-th divided surface on the optical axis side from the substantially central position of the divided surface is (ΔnL) π (rad), and the light transmitted through the (2n + 1) -th divided surface and the central position Light transmitted through the second n-th divided surface on the side opposite to the optical axis side,
Is (ΔnH) π (rad), then (Δn
H) An objective lens of an optical pickup device, which satisfies ≠ (ΔnL).

(22) The first optical information recording medium having a transparent substrate thickness of t1 and the transparent substrate having a thickness of t2 (where t2 ≠
The light beam emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system with respect to the second optical information recording medium of t1), and the information is recorded on the information recording surface or the information is recorded on the information recording surface. In an optical pickup device for reproducing information on a recording surface,
At least one surface of the condensing optical system has a plurality of divided surfaces concentrically divided into an optical axis and a plurality of divided surfaces, and is closer to the optical axis than a second n-th divided surface (where n is an integer of 1 or more). The light transmitted through the transparent substrate through the (2n-1) -th divided surface and the transparent substrate transmitted through the second n-divided surface on the optical axis side from a substantially central position of the 2n divided surface in a direction orthogonal to the optical axis. The phase difference between the light passing through is represented by (ΔnL) π (rad),
Light passing through the (2n + 1) -th divided surface on the opposite side to the optical axis side from the second n-divided surface and passing through the transparent substrate, and transmitting through the second n-divided surface opposite to the optical axis side from the center position. An optical pickup device satisfying (ΔnH) ≠ (ΔnL), where (ΔnH) π (rad) represents a phase difference between light passing through the transparent substrate.

(23) Transparent substrate thickness t1, refractive index n
No. 1 first optical information recording medium and a second optical information recording medium having a transparent substrate thickness t2 (where t2 ≠ t1), a refractive index n2, and a recording density smaller than that of the first optical information recording medium. In the light-collecting optical system of the optical pickup device capable of recording or reproducing the optical information recording medium, the light flux from the recording or reproducing light source of the first optical information recording medium is converted into a transparent light having a thickness t1 and a refractive index n1. When condensing via a substrate to form a beam spot for recording or reproduction of the first optical information recording medium,
From the optical information recording medium side, the numerical aperture NAL to the numerical aperture N
AH (where NAH> NAL) does not converge at the beam spot forming position, and the light from a recording or reproducing light source of the second optical information recording medium is transferred to a thickness t.
2. When light is condensed through a transparent substrate having a refractive index of n2 to form a beam spot for recording or reproduction on the second optical information recording medium, N is viewed from near the optical axis when viewed from the optical information recording medium side.
At least one surface of the condensing optical system is so arranged that a light beam up to AH is condensed at the beam spot forming position and a light beam in a region having a higher NA than NAH is not condensed at the beam spot forming position. A condensing optical system for an optical pickup device, comprising a plurality of divided surfaces concentric with an optical axis.

(24) In a condensing optical system of an optical pickup device capable of recording or reproducing information on or from two types of optical information recording media having different thicknesses and recording densities of a transparent substrate, a light beam emitted from a light source is focused on an optical axis. At least one surface of the condensing optical system is divided concentrically with the optical axis so as to be divided into at least three light beams of a first light beam, a second light beam, and a third light beam in order from the vicinity of the optical axis in the vertical direction. When recording or reproducing on an optical information recording medium having a low recording density, the first light flux and the second light flux near the optical axis of the light flux emitted from the light source are recorded on the optical information recording medium. When recording or reproducing on an optical information recording medium having a large recording density by condensing light onto a surface, the first light beam and the third light beam among the light beams emitted from the light source are applied to the information recording surface of the optical information recording medium. Light that is focused Condensing optical system of the pickup device.

[0080]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. When the same components are used, the same numbers are given. Further, in this specification, a converging optical system (objective lens) required for recording or reproducing data on or from a first optical information recording medium (also referred to as a first optical disk) having a thickness t1 of a transparent substrate is provided on the optical information recording medium side. A condensing optical system (objective lens) required for recording or reproducing a second optical information recording medium (also referred to as a second optical disc) having a numerical aperture NA1 of a thickness t2 of a transparent substrate.
Is larger than the numerical aperture NA2 on the optical information recording medium side (NA
2 <NA1).

(First Embodiment) Before describing the first embodiment, an optical pickup device will be described. FIG. 1 is a schematic configuration diagram of an optical pickup device.

The optical pickup device 10 includes a semiconductor laser 11 (wavelength λ = 610 to 670 nm) as a light source, a polarizing beam splitter 12, a collimator lens 13, and a 1/4.
A wavelength plate 14, a diaphragm 17, an objective lens 16, a cylindrical lens 18 as an astigmatism element that generates astigmatism,
It comprises a photodetector 30, a two-dimensional actuator 15 for focus control and tracking control, and the like.

The light beam emitted from the semiconductor laser 11 is divided into a polarized beam splitter 12, a collimator lens 13,
The light passes through the four-wavelength plate 14 to become a circularly polarized parallel light beam. This light beam is stopped down by the stop 17, and the information recording surface 2 is passed through the transparent substrate 21 of the optical disc 20 by the objective lens 16.
2 are collected. The light flux modulated and reflected by the information pits on the information recording surface 22 is returned to the objective lens 1.
The light passes through the 6, 1/4 wavelength plate 14 and the collimator lens 13, enters the polarization beam splitter 12, is reflected there, is given astigmatism by the cylindrical lens 18, is incident on the photodetector 30, and detects light. A read (reproduction) signal of information recorded on the optical disc 20 is obtained by using a signal output from the device 30. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed. That is, using the output from the photodetector 30, a focus error signal and a tracking error signal are generated by an arithmetic processing circuit (not shown). Based on the focus error signal, the two-dimensional actuator (for focus control) 15 transmits light from the semiconductor laser 11 to the information recording surface 2 of the optical disc 20.
The objective lens 16 is moved in the optical axis direction so as to form an image on the semiconductor laser 2, and a two-dimensional actuator (for tracking control) 15 is operated based on the tracking error signal.
The objective lens 16 is moved in a direction perpendicular to the optical axis so that the light from 1 is focused on a predetermined track.

In such an optical pickup device 10, a first optical disk having a transparent substrate with a thickness of t1, for example, D
When reproducing VD (t1 = 0.6 mm), the objective lens 16 is driven by the two-dimensional actuator 15 so that the beam spot forms a minimum circle of confusion (best focus). Using this objective lens 16, a second optical disc having a recording density lower than that of the first optical disc at t2 (preferably t2> t1) where the thickness of the transparent substrate is different from t1;
For example, when reproducing a CD (t2 = 1.2 mm), the thickness of the transparent substrate differs (preferably increases), spherical aberration occurs, and the position (paraxial focus) where the beam spot becomes a circle of least confusion. (A position behind the position), the spot size is large and pits (information) on the second optical disc cannot be read (reproduced). However, at the front position (front pin) closer to the objective lens 16 than the position of the minimum circle of confusion, although the size of the entire spot is larger than the minimum circle of confusion, the nucleus where the light amount is concentrated in the center and the nucleus around Flare, which is unnecessary light, is formed. This nucleus is used for reproducing (reading) pits (information) of the second optical disk, and at the time of reproducing the second optical disk, the two-dimensional actuator 15 is driven so that the objective lens 16 is in a defocused (front focus) state. .

Next, in order to reproduce the first optical disk and the second optical disk having different thicknesses of the transparent substrate as described above with one condensing optical system, one of the condensing optical systems of the optical pickup device 10 is used. A first embodiment in which the present invention is applied to a certain objective lens 16 will be described. FIG. 2 is a sectional view (a) schematically showing the objective lens 16 and a front view (b) viewed from the light source side. The dashed line indicates the optical axis. In the present embodiment, the thickness t1 of the transparent substrate of the first optical disk is smaller than the thickness t2 of the transparent substrate of the second optical disk, and the first optical disk records information at a higher density than the second optical disk. Have been.

In the present embodiment, the objective lens 16
Is a convex lens having a positive refractive power, both of the refracting surface S1 on the light source side and the refracting surface S2 on the optical disk 20 side having an aspherical shape. In addition, the refracting surface S of the objective lens 16 on the light source side
Reference numeral 1 denotes a plurality (three in the present embodiment) of first divided surfaces Sd1 to third divided surfaces Sd3 concentric with the optical axis. Steps are provided at the boundaries between the divided surfaces Sd1 to Sd3 to form the respective divided surfaces Sd1 to Sd3. In the objective lens 16, a light beam (first light beam) passing through the first division surface Sd1 including the optical axis is used for reproducing information recorded on the first optical disk and reproducing information recorded on the second optical disk. Second divided surface Sd outside first divided surface Sd1
The light beam (second light beam) passing through the second optical disc 2 is mainly used for reproducing information recorded on the second optical disc, and the light beam (third light beam) passing through the third split surface Sd3 outside the second split surface Sd2 is The shape is such that it is mainly used for reproducing information recorded on the first optical disc.

Here, the meaning of the word “mainly” means that in the case of a light beam passing through the second division surface Sd2, the third division surface Sd
In contrast to the energy of the core portion at the position where the center intensity of the beam spot is maximized in a state where the light beam passing through No. 3 is not blocked, the center intensity of the beam spot in a state where the light beam passing through the third division surface Sd3 is blocked The energy ratio of the nuclear portion at the maximum position (“nuclear energy in the light-shielded state” / “nuclear energy in the light-shielded state”) is 60% to 1%.
00%. Similarly, in the case of a light beam passing through the third division surface Sd3,
This indicates that the energy ratio of the light-shielded nuclear portion to the light-shielded state of d2 (“shielded nuclear energy” / “non-shielded nuclear energy”) falls within the range of 60% to 100%. In order to simply measure the energy ratio, in each case, the peak intensity Ip at the position where the center intensity of the beam spot is maximum,
The beam diameter Dp (determined at a position where the intensity is e ⁻² with respect to the center intensity) is measured, and since the shape of the beam at the core is almost constant, Ip × Dp may be obtained and compared. .

As described above, the light beam emitted from the light source is
The first light flux near the optical axis of the focusing optical system is used for reproducing the first optical disc and the second optical disc, and the second light flux outside the first light flux is mainly used for reproducing the second optical disc. By using the third light beam outside the two light beams mainly for reproduction of the first optical disk, the light from the light source can be reduced by a single condensing optical system while suppressing the loss of the light amount (in the present embodiment, two or more light beams are emitted).
) Can be reproduced. Moreover, in this case, most of the third light flux is unnecessary light during reproduction of the second optical disk, but since this unnecessary light is not used for reproduction of the second optical disk, the aperture 17 is set to an aperture required for reproduction of the first optical disk. By simply setting the numerical value, reproduction can be performed without any means for changing the numerical aperture of the diaphragm 17.

More specifically, the objective lens 16 in the present embodiment, when reproducing the first optical disc (see FIG. 2A), has the first divided surface Sd1 and the third divided surface Sd1.
The first light beam and the third light beam passing through d3 (light beams indicated by oblique lines) are imaged at substantially the same first imaging position, and their wavefront aberrations (excluding the second light beam passing through the second division surface Sd2) Wavefront aberration) is 0.05λrms or less. Here, λ is the wavelength of the light source.

At this time, the second light beam (light beam shown by a broken line) passing through the second division surface Sd2 forms an image at a second image forming position different from the first image forming position. If the first imaging position is 0 (zero) and the objective lens 16 side is negative and the opposite side is positive, the second imaging position is at a distance of not less than -27 μm and not more than -4 μm from the first imaging position. (The second imaging position is closer to the objective lens than the first imaging position). As a result, the reproduction of the first optical disk is mainly performed by the first light beam and the third light beam. If the lower limit (−27 μm) is exceeded, the spherical aberration will be excessively corrected, the spot shape during reproduction of the first optical disc will be deteriorated, and the upper limit (−27 μm) will not be obtained.
If it exceeds 4 μm), the spot diameter and side lobe at the time of reproduction of the second optical disk become large. In the present embodiment, since t1 <t2 and NA1> NA2, the second imaging position is set to −27 μm to −4 μm from the first imaging position. However, when t1> t2 and NA1> NA2, , The second imaging position is set to 4 μm to 27 μm from the first imaging position. That is, the absolute value of the distance between the first imaging position and the second imaging position is 4
It is set to be in the range of not less than μm and not more than 27 μm.

When the objective lens 16 is used for reproducing a second optical disk having a transparent substrate having a predetermined thickness (t2 = 1.2 mm), as shown in FIG. In the case of an incident predetermined light beam (parallel light beam), the first light beam (shown by oblique lines rising upward to the right) passes through the optical axis at a position where a light ray passing near the optical axis intersects with the optical axis and in a direction orthogonal to the optical axis. The light beam of the second light flux (indicated by the oblique line inclined downward to the left) intersects with the optical axis between the end of the split surface Sd1 (the second split surface Sd2 side) and the position where the light beam intersects the optical axis (imaging). Do). Therefore, the first light beam and the second light beam are collected near the information recording surface of the second optical disk, and the reproduction of the second optical disk is performed. At this time, the third light beam (shown partly by a broken line) is generated as a flare, but the nucleus formed by the first light beam and the second light beam makes it possible to reproduce the second optical disc.

In other words, according to the present invention, the first light beam passing near the optical axis having a small numerical aperture is used for reproducing all reproducible optical disks, and the light beam passing outside the first division surface is reproduced. Each of the divided light beams is used to reproduce each optical disk (first and second optical disks in the present embodiment) so as to correspond to each optical disk to be reproduced. At this time, the light beam used for reproducing the optical disk (first optical disk in the present embodiment) having the larger numerical aperture required for reproducing the information on the optical disk is separated from the first light beam among the divided light beams. It is a light beam (third light beam in the present embodiment).

When such a condensing optical system (the objective lens 16 in this embodiment) is used, it is possible to reproduce a plurality of optical discs having different thicknesses of the transparent substrate with one condensing optical system. In addition, since the surface can be set arbitrarily, the numerical aperture NA2 required for reproducing the second optical disc can be increased. Further, a light beam near the optical axis (first light beam)
Is used for reproducing a plurality of optical disks, the loss of light quantity of the light beam from the light source is reduced. In addition, at the time of reproducing the second optical disc, the side lobe of the beam spot is reduced, a nucleus having a strong beam intensity is formed, and accurate information can be obtained. Further, a plurality of optical discs can be reproduced by one condensing optical system without requiring any special means for changing the numerical aperture of the stop 17.

In the present embodiment, when viewed at the center of the second division surface Sd2 (see FIG. 2A) in a direction orthogonal to the optical axis, the second surface Sd2 is a surface from the numerical aperture NAL to the numerical aperture NAH. The angle formed between the normal line of the two-divided surface Sd2 and the optical axis is a first divided surface Sd1 which is a surface from the optical axis to the numerical aperture NAL, and a third divided surface Sd3 which is a surface from the numerical aperture NAH to the numerical aperture NA1. (Aspherical surface fitted by the least squares method using the aspherical expression of Equation 1 described later)
Greater than the angle between the normal to the optical axis. As a result, it is possible to satisfactorily reproduce both the first optical disk and the second optical disk. In the present embodiment, t2
> T1, NA1> NA2, so the second division surface Sd2
Angle between the normal and the optical axis is the first or third divided surface Sd1,
Although the angle is larger than the angle between the optical axis and the normal line of the interior surface from Sd3, it may be smaller in the case of t2 <t1, NA1> NA2.

Further, in the present embodiment, in the direction orthogonal to the optical axis, a substantially central position of the second divided surface Sd2 (FIG. 2)
(A), the angle between the normal line of the second divided surface Sd2 and the optical axis, the first divided surface Sd1, and the third divided surface S
The difference between the normal line of the surface interpolated from d3 (the aspheric surface subjected to fitting by the least-squares method using the aspheric surface expression of Equation 1 described later) and the angle formed by the optical axis is 0.02 ° or more. It is preferable to set the first divided surface Sd1 to the third divided surface Sd3 so as to be in a range of 1 ° or less. If the lower limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, and the side lobe spot diameter increases. If the upper limit is exceeded, spherical aberration is excessively corrected, and the spot shape during reproduction of the first optical disc deteriorates.

When the present embodiment is viewed from another point of view, at least one surface is divided into a plurality of divided surfaces concentrically with the optical axis (three divided surfaces in the present embodiment).
In the objective lens 16 having the above, the light transmitted through the first split surface Sd1 on the optical axis side from the second split surface Sd2 and the third split surface Sd3 on the opposite side of the optical axis side from the second split surface Sd2. When the light and the light pass through the transparent substrate having a predetermined thickness (first optical disk) and have substantially the same phase, the light passing through the first division surface Sd1 and passing through the transparent substrate is orthogonal to the optical axis. The phase difference between the light passing through the second divided surface Sd2 on the optical axis side from the substantially central position of the second divided surface Sd2 (see FIG. 2A) and passing through the transparent substrate in the direction of the second divided surface Sd2 is (Δ1L) π ( ra
d), the position of the light passing through the third divided surface Sd3 and passing through the transparent substrate and the light passing through the second divided surface Sd2 opposite to the optical axis side from the center position and passing through the transparent substrate. The phase difference is (Δ
1H) π (rad), (Δ1H)> (Δ1L)
To be satisfied. In this case, the sign of the phase difference is such that the traveling direction of the light (the direction toward the optical disk) is positive, and the second division surface for the light transmitted through the first division surface Sd1 or the third division surface Sd3 and transmitted through the transparent substrate. The phase difference of light passing through Sd2 and passing through the transparent substrate is compared. In this embodiment, since t1 <t2 and NA1> NA2, (Δ1H)>
(Δ1L), but when t1> t2 and NA1> NA2, (Δ1H) <(Δ1L). Therefore,
(Δ1H) ≠ (Δ1L).

From another point of view, the first division plane S
First division plane S at the boundary between d1 and second division plane Sd2
The step amount from the third division surface Sd3 at the boundary between the third division surface Sd3 and the second division surface Sd2 is larger than the step amount from d1 (the sign of the step amount is refracted at the division surface as a boundary). The direction in which the rate changes from small to large is assumed to be positive. Also in this case, similarly to the above, when t1> t2 and NA1> NA2, the above relationship is reversed, that is, the first divided surface Sd of the two divided surfaces Sd2.
From the step amount from 1, the third division surface S of the second division surface Sd2
The step difference from d3 is smaller. Further, at a predetermined position from the optical axis, the position of a surface interpolated from the first divided surface Sd1 and the third divided surface Sd3, and the position of the second divided surface Sd2
Is preferably asymmetrical about the substantially central position of the second division surface Sd2. further,
In this case, it is preferable that the difference increases as the distance from the optical axis increases.

In this embodiment, the dividing planes Sd1 to Sd1
Although Sd3 is provided on the refracting surface S1 on the light source side of the objective lens 16, it may be provided on the refracting surface on the optical disk 20 side.
One of the optical elements of another condensing optical system (for example, the collimator lens 13) may have such a function,
Further, an optical element having such a function may be newly provided on the optical path. Further, the functions of the respective divided surfaces Sd1 to Sd3 may be provided by being disassembled into different optical elements.

Further, in this embodiment, the so-called infinite system objective lens 16 using the collimator lens 13 is used. However, since the collimator lens 13 is not provided, the divergent light from the light source is directly or the degree of divergence of the divergent light is reduced. The present invention may be applied to an objective lens in which divergent light through a lens enters, or a coupling lens that changes a light flux from a light source into convergent light and the convergent light enters.

In the present embodiment, the first division surface Sd
Although a step is provided at the boundary between the first to third division surfaces Sd3, a division surface may be formed continuously without providing a step at at least one boundary. In addition, the boundary between the divided surfaces may be connected by, for example, a surface having a predetermined radius of curvature without bending the boundary.

In the present embodiment, the refractive surface S1 is 3
Although the configuration is made up of the three division planes Sd1 to Sd3, the invention is not limited to this, and it is sufficient if it is composed of at least three or more division planes. In this case, a first division surface used for reproducing the first optical disk and the second optical disk is provided near the optical axis, and the division surface outside the first division surface (in the direction away from the optical axis) is mainly the second division surface.
It is preferable to alternately provide a division surface used for reproducing the optical disk and a division surface mainly used for reproducing the first optical disk. In this case, 0.60 (NA2) <NA3 <
1.3 (NA2), 0.01 <NA4-NA3 <0.1
It is preferable to provide a division surface mainly used for reproducing the second optical disk between the numerical aperture NA3 and the numerical aperture NA4 on the optical disk side of the objective lens 16 that satisfies the condition 2. Thus, an optical disk having a larger required numerical aperture as the second optical disk can be reproduced without lowering the intensity of the light spot focused on the first optical disk. Further, it is practically preferable that the upper limit of NA3 is NA3 <1.1 (NA2), and the lower limit of NA3 is 0.80 (N
A2) <NA3 is preferable, and 0.85 (NA2) is more preferable.
<NA3 is practically preferable. NA4-
The upper limit of NA3 is preferably NA4−NA3 <0.1.

In the present embodiment, a plurality of optical disks are reproduced using one light source. However, a plurality of light sources may be used for each optical disk to be reproduced.

In the present embodiment, when the objective lens 16 is viewed from the light source side, the second division surface Sd2 is provided in a ring shape concentric with the optical axis. However, the present invention is not limited to this. May be provided. Further, the second division surface Sd2 may be formed of a hologram or Fresnel. Note that the second division surface S
When d2 is configured as a hologram, one of the light beams divided into the 0th-order light and the 1st-order light is used for reproducing the first optical disk, and the other is used for reproducing the second optical disk. At this time, the second
It is preferable that the light amount of the light beam used for reproducing the optical disk is larger than the light amount of the light beam used for reproducing the first optical disk.

In the present embodiment, when reproducing the first optical disk (ie, when passing through the transparent substrate having the thickness t1), the best wavefront due to the light beam passing through the first divided surface Sd1 and the third divided surface Sd3. The aberration not only satisfies 0.05λrms (where λ (nm) is the wavelength of the light source used when reproducing the first optical disk), but also when reproducing the second optical disk (that is, the transparent film having the thickness t2). The best wavefront aberration due to the light beam passing through the first division surface Sd1 (when passing through the substrate) is 0.07λrms (where λ (nm) is the wavelength of the light source used when reproducing the second optical disk), which is the diffraction limit. By satisfying the condition, the reproduction signal of the second optical disc can be improved.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. 4, which is a diagram schematically showing a spherical aberration diagram of the objective lens 16. In FIG. 4, (a) reproduces the first optical disk, that is, the thickness t
FIG. 4B is a spherical aberration diagram when the light passes through the transparent substrate of FIG.
FIG. 7 is a spherical aberration diagram when reproducing the second optical disc, that is, when passing through a transparent substrate having a thickness t2 (t2> t1 in the present embodiment). Here, the necessary numerical aperture on the optical disc side of the condensing optical system necessary for reproducing the information on the first optical disc is NA1, and the necessary numerical aperture on the optical disc side of the condensing optical system necessary for reproducing the information on the second optical disc is described. The numerical aperture is NA2 (where NA2> NA1), and the division surface Sd of the objective lens 16
The numerical aperture on the optical disk side of the light beam passing through the boundary between 1 and Sd2 is NAL, and the divided surfaces Sd1 and Sd2 of the objective lens 16 are
The numerical aperture on the optical disk side of the luminous flux passing through the boundary with
L.

The second embodiment is different from the first embodiment described above.
FIG. 14 is a view of the objective lens 16 described in the embodiment from another viewpoint (spherical aberration, shape, wavefront aberration, and the like);
Parts not described below are the same as in the first embodiment.

In the objective lens 16 as described in the first embodiment, first, the best wavefront aberration of the light beam condensed on the first optical disc having a transparent substrate thickness t1 is 0.05λrm.
s or less and the first aspherical surface of the first refraction surface S1 and the second
The refraction surface S2 (common refraction surface) is designed. FIG. 4C shows a spherical aberration diagram of the lens obtained by this design. Then, the spherical aberration when condensed on the second optical disk having the thickness t2 (t2 ≠ t1) of the transparent substrate via the lens having the first aspheric surface (FIG. 4E, in this case, t2> t1) The second refracting surface S2 (common refracting surface) is designed as it is and the second aspherical surface of the first refracting surface is designed so that the spherical aberration is smaller than the amount of occurrence of (1). At this time, it is preferable that the paraxial radius of curvature of the second aspherical surface and the paraxial radius of curvature of the first aspherical surface be the same in order to perform good reproduction of the second optical disc that is reproduced in a defocused state. FIG. 4 shows a spherical aberration diagram when the lens obtained by this design is focused on the second optical disc.
FIG. 4F is an aberration diagram of the lens when the light is focused on the first optical disk by this lens. Then, the required numerical aperture N of the second optical disk having the first aspheric surface
A second aspherical surface is synthesized near A2. Here, the vicinity of the required numerical aperture NA2 for synthesizing the second aspherical surface is 0.60 (N
A2) Condition of <NA3 <1.3 (NA2) (The lower limit of 0.60 (NA2) is practically preferably 0.80 (NA2), more preferably 0.85 (NA2). This upper limit 1.3 (NA2) is practically 1.1.
(Preferably NA2)) and the numerical aperture NA3 and the numerical aperture on the optical disk side of the objective lens 16 satisfying the condition of 0.01 <NA4−NA3 <0.12 (preferably 0.1). It is preferably between several NA4. The side closer to the optical axis in the synthesized second aspherical surface (second division surface) is the numerical aperture NAL, and the far side is the NAH (that is, NAL <NAH).

Therefore, the surface shape of the refraction surface S1 of the objective lens 16 is the first division surface S including the optical axis.
d1 and the third divided surface Sd3 outside the first divided surface Sd1 have the same aspherical shape (first aspherical surface), and between the first divided surface Sd1 and the third divided surface Sd3 (reproduction of the second optical disk) Near the numerical aperture NA2 required for
The second divided surface Sd2 of AH) has an aspherical shape (second aspherical surface) different from the first divided surface Sd1 and the third divided surface Sd3. The obtained lens is the objective lens 16 of the present embodiment.
FIG. 4A shows the spherical aberration when the light is focused on the first optical disk by using the objective lens 16.
FIG. 4B shows the spherical aberration when the light is focused on the optical disk.
Becomes

When the first aspherical surface and the second aspherical surface are combined, the second divided surface Sd2 is combined shifted in the direction of the optical axis, and the phase difference is used to collect the data at the time of reproducing the first optical disk. The amount of light can be increased.

In the present embodiment, the expression of the aspherical surface is:

[0111]

(Equation 1)

[0112] Where X is the axis in the direction of the optical axis, H is the axis perpendicular to the optical axis, and the traveling direction of light is positive, r is the paraxial radius of curvature, K is the conic coefficient, Aj is the aspherical coefficient, and Pj is the aspherical surface. (Where Pj ≧ 3). In the present invention, other aspherical expressions other than the above expression may be used. In addition, when calculating the expression of the aspherical surface from the aspherical shape, the above expression is used, Pj is determined as a natural number of 3 ≦ Pj ≦ 10, and Κ = 0.

As described above, the objective lens 16 obtained in the present embodiment uses a plurality of optical disks having different thicknesses of the transparent substrate at at least two opening positions (NAL and NAH) near the numerical aperture NA2. It is configured so that the spherical aberration changes discontinuously so that it can be reproduced by one condensing optical system. Since the spherical aberration is changed discontinuously in this manner, the range of each numerical aperture (in the present embodiment, the first division plane from the optical axis to the NAL, the second division plane from NAL to NAH, the NAH to The luminous flux (first luminous flux to third luminous flux in the present embodiment) passing through the third division surface of NA1 can be arbitrarily configured, and is used for reproducing all of a plurality of optical discs for reproducing the first luminous flux. Each of the second light beam and the third light beam can be used for reproducing a predetermined optical disk among the plurality of optical disks, and a plurality of optical disks can be reproduced by one condensing optical system (the objective lens 16 in the present embodiment). It can be realized at low cost and without complication, and can also handle optical disks with a high NA. Moreover, the aperture 17
Need only be provided so as to correspond to NA1, which is a high NA, and even if the numerical aperture (to NA1 or NA2) necessary for reproducing the optical disk changes, there is no need to provide any means for changing the aperture 17. In the present invention, "the spherical aberration changes discontinuously" means that a sharp change in the spherical aberration is observed when viewed in a spherical aberration diagram.

Further, the direction in which the spherical aberration changes discontinuously when viewed from a small numerical aperture to a large numerical aperture is such that the spherical aberration is negative in the numerical aperture NAL and positive in the numerical aperture NAH. In the direction of As a result, the reproduction of the optical disk having the thin transparent substrate thickness t1 becomes good, and the reproduction of the optical disk having the transparent substrate thickness t2 larger than that can be performed satisfactorily. In this embodiment, since t2> t1 and NA1> NA2, the spherical aberration changes discontinuously in the negative direction at the numerical aperture NAL and in the positive direction at the numerical aperture NAH as described above. , T2 <
When t1, NA1> NA2, the spherical aberration changes discontinuously in the positive direction at the numerical aperture NAL and in the negative direction at the numerical aperture NAH.

Further, when reproducing the second optical disk having the thickness t2 of the transparent substrate, the numerical aperture NAL is changed to the numerical aperture NAH.
By making the spherical aberration (spherical aberration due to the light beam passing through the second division surface Sd2) during the period up to positive, the S-shaped characteristic of the optical pickup device 10 is improved. In this embodiment, since t2> t1 and NA1> NA2, the spherical aberration from the numerical aperture NAL to the numerical aperture NAH is made positive. However, t2 <t1, NA1> NA2.
In the case of, it is good to make it negative.

Further, when passing through a transparent substrate having a thickness t1 (see FIG. 4 (a)), the numerical aperture is smaller than NA1.
The luminous flux passing between L and NAH is excluded, that is, the wavefront aberration due to the luminous flux passing through the optical axis -NAL and NAH-NA1 is set to 0.05 [lambda] rms or less (where [lambda] is the wavelength of the light source). The first thickness of the substrate is t1
The reproduction of the optical disk is improved.

Further, t1 = 0.6 mm, t2 = 1.2 m
m, 610 nm <λ <670 nm, 0.32 <NA2 <
Assuming 0.41, 0.60 (NA2) <NAL <
1.3 (NA2) condition (the lower limit is 0.60 (NA2)
Is practically preferably 0.80 (NA2), and more preferably 0.80 (NA2).
It is preferably 85 (NA2). In addition, it is preferable that the upper limit 1.3 (NA2) is practically 1.1 (NA2). If the lower limit is exceeded, the side lobes become too large to allow accurate reproduction of information, and if the upper limit is exceeded, the diameter is too narrow to exceed the diffraction limit spot diameter assumed at wavelengths λ and NA2. The NAL referred to here indicates the NAL on the second division surface Sd2.

In addition, 0.01 <NAH-NAL <0.1
It is preferable to satisfy the condition of 2 (the upper limit of 0.12 is practically more preferably 0.1). If the lower limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, the side lobe spot diameter increases, and if the upper limit is exceeded, the spot shape during reproduction of the first optical disc is disturbed,
This causes a decrease in the amount of light. Note that NAL and NAH here are the NAL and NAH on the second division surface Sd2.
Point to.

From another point of view (again, again), 0.60 (NA2) <NA3 <1.3 (NA2)
(The lower limit of 0.60 (NA2) is practically 0.8
0 (NA2), more preferably 0.85 (NA2), and the upper limit of 1.3 (NA2).
Is practically preferably 1.1 (NA2)), and 0.01 <NA4-NA3 <0.12.
Objective lens 1 satisfying the condition (preferably 0.1)
The NAL and NAH described above are provided between the numerical apertures NA3 and NA4 on the optical disk side of No. 6 (that is, a division surface mainly used for reproducing the second optical disk is provided).
As a result, an optical disk having a larger required numerical aperture as the second optical disk can be reproduced without significantly reducing the intensity of the light spot focused on the first optical disk.

During reproduction of the second optical disc (through the transparent substrate having a thickness of t2), the spherical aberration between the numerical aperture NAL and the numerical aperture NAH is -2λ / (NA2) ² or more.
It is preferable to satisfy the condition of 5λ / (NA2) ² or less. Furthermore, this condition is 3λ / (NA
2) It is preferable that ² is as follows, or it is preferable to be larger than 0 (zero) in consideration of recording (of course, reproduction is possible). If the lower limit is exceeded, the spherical aberration is excessively corrected, and the spot shape during reproduction of the first optical disc deteriorates. If the upper limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, and the side lobe spot diameter increases. In particular, it is more preferable that this condition satisfies the range of 0 to 2λ / (NA2) ^{2. In} this case, a good focus error signal can be obtained.

On the other hand, in the present embodiment, when viewed at the center of the second division surface Sd2 in a direction perpendicular to the optical axis, the angle formed by the normal line of the second division surface Sd2 and the optical axis is the first division surface. Sd
The angle is larger than the angle between the optical axis and the normal to the plane interpolated from the first and third division planes Sd3. As a result, it is possible to satisfactorily reproduce both the first and second optical disks. In the present embodiment, t2> t1, NA
Since 1> NA2, the angle between the normal to the second divided surface Sd2 and the optical axis is larger than the angle between the normal to the surface embedded from the first and third divided surfaces Sd1 and Sd3 and the optical axis. But
In the case of t2 <t1, NA1> NA2, the value may be small.

Further, the objective lens 16 of the present embodiment has a numerical aperture NAL and a numerical aperture N in a direction orthogonal to the optical axis.
When viewed at a substantially central position of AH (second division plane Sd2),
Surface from numerical aperture NAL to numerical aperture NAH (second division surface)
Angle between the normal to the optical axis, the plane from the optical axis to the numerical aperture NAL (first division plane), and the numerical aperture NAH to the numerical aperture NA
The angle between the optical axis and the normal to the surface (the aspheric surface fitted by the least squares method using the above-described aspheric surface expression of Equation 1) interpolated from the surface up to 1 (third divided surface) Is the difference
It is preferable that the angle be in the range of 0.02 ° to 1 °.
If the lower limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, the side lobe spot diameter increases,
When the value exceeds the upper limit, the spherical aberration is excessively corrected, and the spot shape at the time of reproducing the first optical disc deteriorates.

In particular, t2> t1, NA1> NA2
When viewed from the optical axis in the circumferential direction, at the numerical aperture NAL, the intersection of the optical axis with the normal to the refraction surface changes discontinuously in a direction approaching the refraction surface on the light source side. The intersection between the normal line of the refraction surface and the optical axis changes discontinuously in a direction away from the refraction surface on the light source side. As a result, the reproduction of the optical disk having the thin transparent substrate thickness t1 becomes good, and the reproduction of the optical disk having the transparent substrate thickness t2 larger than that can be performed satisfactorily.

As in the case of the first embodiment described above, when the present embodiment is taken from another viewpoint, a plurality of divided surfaces (at least one surface of which is divided concentrically with the optical axis). In the objective lens 16 having three divided surfaces in the present embodiment), the light transmitted through the first divided surface Sd1
When the light transmitted through the third division surface Sd3 is made to have substantially the same phase via the transparent substrate (of the first optical disk) having a predetermined thickness, the light is transmitted through the first division surface Sd1 and the transparent substrate is The phase difference between the transmitted light and the light transmitted through the transparent substrate through the second divided surface Sd2 on the optical axis side from the substantially central position of the second divided surface Sd2 is (Δ1L) π (rad), The phase difference between the light transmitted through the divided surface Sd3 and passing through the transparent substrate and the light transmitted through the second divided surface Sd2 on the side opposite to the optical axis side from the center position and transmitted through the transparent substrate is (Δ1H) π. (Rad)
Then, (Δ1H)> (Δ1L) is satisfied. In addition,
In the present embodiment, since (t1 <t2, NA1> NA2), (Δ1H)> (Δ1L), but t1> t2, N
When A1> NA2, (Δ1H) <(Δ1L). Therefore, (Δ1H) ≠ (Δ1L).

From another point of view, the second division plane S
The step amount of the second division surface Sd2 from the third division surface Sd3 is larger than the step amount of d2 from the first division surface Sd1. Also in this case, similarly to the above, t1> t2, NA1> N
In the case of A2, the third division surface at the boundary between the third division surface Sd3 and the second division surface Sd2 is obtained from the step amount from the first division surface Sd1 at the boundary between the first division surface Sd1 and the second division surface Sd2. The level difference from Sd3 is smaller. Further, at a predetermined position from the optical axis, the difference between the position of the surface interpolated from the first divided surface Sd1 and the third divided surface Sd3 and the position of the second divided surface Sd2 is substantially equal to the position of the second divided surface Sd2. Preferably, it is asymmetric about the center position. Further, in this case, it is preferable that the difference increases as the distance from the optical axis increases.

The wavefront aberration of the objective lens 16 according to the present embodiment is as shown in FIG. FIG. 5 is a wavefront aberration curve with the vertical axis representing the wavefront aberration (λ) and the horizontal axis representing the numerical aperture.
(A) is when the transparent substrate (thickness t1) of the first optical disk is interposed, and (b) is the transparent substrate (thickness t1) of the second optical disk.
The wavefront aberration curve when passing through 2) is shown by a solid line.
The wavefront aberration curve is obtained by measuring the wavefront aberration using an interferometer or the like in a state where the wavefront aberration is the best when the light passes through each transparent substrate.

As can be seen from the figure, the objective lens 16 of the present embodiment shows that the wavefront aberration is discontinuous at two locations (specifically, NAL and NAH) near the numerical aperture NA2 when viewed from the wavefront aberration curve. Has become. The maximum discontinuity of the wavefront aberration occurring in the discontinuous portion is 0.05 (NA2) ² (mm) or less and the phase difference unit ( rad), 2π ｛0.05
(NA2) ² ｝ / λ (rad) or less (where λ is the wavelength used and the unit is mm). Above this, the fluctuation of the wavefront aberration due to the wavelength fluctuation becomes large, and it becomes impossible to absorb the fluctuation of the wavelength of the semiconductor laser. Furthermore, this discontinuous part (between NAL and NAH)
Is the slope of the curve (dashed line in FIG. 5A) connecting the ends of the curves on both sides of the discontinuous portion (the end closest to NAL and the end closest to NAH). Have different slopes.

In the present embodiment, the dividing planes Sd1 to Sd1
Although Sd3 is provided on the refracting surface S1 on the light source side of the objective lens 16, it may be provided on the refracting surface on the optical disk 20 side.
One of the optical elements of another condensing optical system (for example, the collimator lens 13) may have such a function,
Further, an optical element having such a function may be newly provided on the optical path. Further, the functions of the respective divided surfaces Sd1 to Sd3 may be provided by being disassembled into different optical elements.

Further, in the present embodiment, the so-called infinite system objective lens 16 using the collimator lens 13 is used. However, since the collimator lens 13 is not provided, the divergent light from the light source is reduced directly or the divergence of the divergent light is reduced. The present invention may be applied to an objective lens in which divergent light through a lens enters, or a coupling lens that changes a light flux from a light source into convergent light and the convergent light enters.

In the present embodiment, the first division surface Sd
Although a step is provided at the boundary between the first to third division surfaces Sd3, a division surface may be formed continuously without providing a step at at least one boundary. Further, the boundary between the divided surfaces may be connected by, for example, a predetermined radius without bending. This R may be provided intentionally or may not be provided intentionally (as an example not provided intentionally, the objective lens 16 is formed of plastic or the like. In some cases, there is a boundary R formed in processing the mold).

In the present embodiment, the refractive surface S1 is set to 3
Although the configuration is made up of the three division planes Sd1 to Sd3, the invention is not limited to this, and it is sufficient if it is composed of at least three or more division planes. In this case, a first division surface used for reproducing the first optical disk and the second optical disk is provided near the optical axis, and the division surface outside the first division surface (in the direction away from the optical axis) is mainly the second division surface.
It is preferable to alternately provide a division surface used for reproducing the optical disk and a division surface mainly used for reproducing the first optical disk. In this case, the smallest numerical aperture among a plurality of divided surfaces (positions at which spherical aberration is discontinuous) is defined as NAL,
Also, considering the largest numerical aperture among a plurality of divided surfaces (positions at which spherical aberration is discontinuous) as NAH, this NAL
And NAH preferably satisfy the above conditions.

Further, in the present embodiment, when the objective lens 16 is viewed from the light source side, the second divided surface Sd2 is provided in a ring shape concentric with the optical axis. However, the present invention is not limited to this. May be provided. Further, the second division surface Sd2 may be formed of a hologram or Fresnel. Note that the second division surface S
When d2 is configured as a hologram, one of the light beams divided into the 0th-order light and the 1st-order light is used for reproducing the first optical disk, and the other is used for reproducing the second optical disk. At this time, the second
It is preferable that the light amount of the light beam used for reproducing the optical disk is larger than the light amount of the light beam used for reproducing the first optical disk.

In this embodiment, when designing the first aspherical surface, as described above, the first aspherical surface passes through the first divided surface Sd1 and the third divided surface Sd3 through the transparent substrate having the thickness t1. The best wavefront aberration caused by the light flux is not more than 0.05 λrms (where λ (nm) is the wavelength of the light source used when reproducing the first optical disk), and the first wavefront aberration when the light is transmitted through the transparent substrate having the thickness t2. The best wavefront aberration due to the light beam passing through the division surface Sd1 is 0.07λrms, which is the diffraction limit.
By design so that λ (nm) is the wavelength of the light source used when reproducing the second optical disk, the reproduction signal of the second optical disk can be improved.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG. 6, which is a schematic configuration diagram of an optical pickup device. In the first and second embodiments, one light source 1 is used as the optical pickup device 10.
In this embodiment, the optical pickup device 10 uses two light sources 111 and 112.

In the present embodiment, at the time of reproducing the first optical disk, the first semiconductor laser 111 serving as the first light source is used.
(Wavelength λ1 = 610 nm to 670 nm), and the second semiconductor laser 11 which is the second light source when reproducing the second optical disc.
2 (wavelength λ2 = 740 nm to 870 nm). The synthesizing unit 19 is a unit capable of synthesizing the light beam emitted from the first semiconductor laser 111 and the light beam emitted from the second semiconductor laser 112, and combines both light beams into one condensing optical system. This is a means for forming the same optical path in order to converge the light on the optical disk 20 through the optical path.

First, when reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111, and the emitted light beam is passed through the combining means 19, the polarizing beam splitter 12, the collimator lens 13, and the quarter-wave plate 14. The transmitted light becomes a parallel light beam of circularly polarized light. This light beam is stopped down by the stop 17 and is focused on the information recording surface 22 by the objective lens 16 via the transparent substrate 21 of the first optical disc 20. The light flux modulated and reflected by the information pits on the information recording surface 22 is again reflected by the objective lens 16, the quarter-wave plate 14,
The light passes through the collimator lens 13 and enters the polarization beam splitter 12, where it is reflected and reflected by the cylindrical lens 1.
8, astigmatism is given, and the light enters the photodetector 30;
Using the signal output from the photodetector 30, a signal for reading (reproducing) information recorded on the first optical disc 20 is obtained. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 15
Moves the objective lens 16 so that the light from the semiconductor laser 11 forms an image on the information recording surface 22 of the first optical disc 20, and moves the objective lens 16 so that the light from the semiconductor laser 11 forms an image on a predetermined track. 16 is moved.

On the other hand, when reproducing the second optical disk, a beam is emitted from the second semiconductor laser 112, and the emitted light flux is changed in optical path by the synthesizing means 19, and thereafter, the polarization beam splitter 12, the collimator lenses 13, 1 /
The second through the four-wavelength plate 14, the diaphragm 17, and the objective lens 16
The light is focused on the optical disk 20. And the information recording surface 2
The light flux modulated and reflected by the information pits in step 2 again enters the photodetector 30 via the objective lens 16, the quarter-wave plate 14, the collimator lens 13, the polarization beam splitter 12, and the cylindrical lens 18, and detects light. A read (reproduction) signal for information recorded on the second optical disc 20 is obtained using the signal output from the recorder 30. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 15 moves the objective lens 16 so that the light from the semiconductor laser 11 is focused on the information recording surface 22 of the second optical disc 20 in a defocused state. The objective lens 16 is moved so that light is focused on a predetermined track.

The objective lens 16 described in the first and second embodiments is used as the objective lens 16 which is one of the condensing optical systems of the optical pickup device 10.
That is, in the objective lens 16, the refracting surface S1 on the light source side and the refracting surface S2 on the optical disc 20 side are both convex lenses having an aspheric shape and having a positive refractive power, and the refracting surface S1 on the light source side has an optical axis. And concentrically (3 in this embodiment)
), The first divided surface Sd1 to the third divided surface Sd3, and the boundary between the divided surfaces Sd1 to Sd3 is provided with a step. The first divided surface Sd1 and the third divided surface Sd3 are the first aspheric surfaces such that the best wavefront aberration of the light beam emitted from the first light source 111 and focused on the first optical disk is 0.05λrms or less. The second divided surface is formed when the light flux of the second light source 112 is condensed on the second optical disk having a thickness of t2 (t2 ≠ t1) through the lens having the first aspheric surface. NAL to NAH, which are formed by the second aspherical surface so as to have a spherical aberration smaller than the amount of spherical aberration generated in the second optical disk of the first aspherical surface in the vicinity of the required numerical aperture NA2.
Then, an objective lens obtained by combining the second aspheric surface is used.

The objective lens 16 obtained in the present embodiment has the same configuration, operation and effects as those of the above-described second embodiment except for the following points. Therefore, the degree of freedom in reproducing a plurality of optical disks is increased.

In this embodiment, two light sources 111 and 11
2, the following preferred range is different from that of the second embodiment.

That is, t1 = 0.6 mm, t2 = 1.
2 mm, 610 nm <λ1 <670 nm, 740 nm <
When λ2 <870 nm and 0.40 <NA2 <0.51, 0.60 (NA2) <NAL <1.1 (NA2)
(The lower limit of 0.60 (NA2) is practically 0.8
0 (NA2) is preferable, and more preferably 0.85 (NA2) is satisfied. If the lower limit is exceeded, the side lobes become too large to allow accurate reproduction of information, and if the upper limit is exceeded, the diameter is too narrow to be greater than the diffraction limit spot diameter assumed at wavelengths λ2 and NA2. In addition,
The NAL here is the second value when the second light source 112 is used.
NAL on the division surface Sd2.

Further, 0.01 <NAH-NAL <0.1
It is preferable to satisfy the condition of 2 (the upper limit of 0.12 is practically more preferably 0.1). If the lower limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, the side lobe spot diameter increases, and if the upper limit is exceeded, the spot shape during reproduction of the first optical disc is disturbed,
This causes a decrease in the amount of light. Note that NAL and NAH referred to here are the second division planes S when the second light source 112 is used.
Refers to NAL and NAH on d2.

During reproduction of the second optical disc (through the transparent substrate having a thickness of t2), the spherical aberration between the numerical aperture NAL and the numerical aperture NAH is -2 (λ2) / (NA2) ²
As described above, it is preferable to satisfy the condition of (5 (λ2)) / (NA2) ² or less. Further, this condition is preferably 3 (λ2) / (NA2) ² for reproduction, or 0 in consideration of recording (of course, reproduction is possible).
It is preferably larger than (zero). If the lower limit is exceeded, the spherical aberration is excessively corrected, and the spot shape during reproduction of the first optical disc deteriorates. If the upper limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, and the side lobe spot diameter increases. In particular, this condition is 0 to 2 (λ2) /
It is more preferable that the range of (NA2) ² is satisfied. In this case, a good focus error signal can be obtained.

From another point of view, 0.60 (N
A2) <NA3 <1.1 (NA2) (the lower limit of 0.60 (NA2) is practically preferably 0.80 (NA2), more preferably 0.85 (NA2)). Together with 0.01 <NA4-NA3 <
The numerical aperture NA3 and the numerical aperture NA on the optical disk side of the objective lens 16 satisfying the condition of 0.12 (preferably 0.1)
4 is provided with the above-described NAL and NAH (that is, provided with a division surface mainly used for reproducing the second optical disc). Thus, an optical disk having a larger required numerical aperture as the second optical disk can be reproduced without lowering the intensity of the light spot focused on the first optical disk.

On the other hand, in the present embodiment, when viewed at the center of the second division surface Sd2 in a direction orthogonal to the optical axis, the angle formed by the normal line of the second division surface Sd2 and the optical axis is the first division surface. Sd
The angle is larger than the angle between the optical axis and the normal to the plane interpolated from the first and third division planes Sd3. As a result, it is possible to satisfactorily reproduce both the first optical disk and the second optical disk. In the present embodiment, t2> t1, NA
Since 1> NA2, the angle between the normal to the second divided surface Sd2 and the optical axis is larger than the angle between the normal to the surface embedded from the first and third divided surfaces Sd1 and Sd3 and the optical axis. But
If t2 <t1, NA1> NA2, the value may be set to a small value.

Further / Furthermore, the objective lens 1 of the embodiment
Reference numeral 6 denotes a circumferential position of the refraction surface S1 of the objective lens 16 corresponding to at least two aperture positions (NAL and NAH) having a numerical aperture near NA2, and the angle between the normal line of the refraction surface and the optical axis is 0. It is preferable that the angle changes from 0.05 degrees to less than 0.50 degrees. If the lower limit is exceeded, the spot shape during reproduction of the second optical disc deteriorates, and the side lobe spot diameter increases. If the upper limit is exceeded, spherical aberration is excessively corrected, and the spot shape during reproduction of the first optical disc deteriorates.

In particular, when t2> t1 and NA1> NA2, when viewed from the optical axis in the circumferential direction, at the numerical aperture NAL, the intersection between the normal of the refraction surface and the optical axis approaches the refraction surface on the light source side. In the numerical aperture NAH, the intersection point between the normal line of the refraction surface and the optical axis changes discontinuously in a direction away from the refraction surface on the light source side. As a result, the reproduction of the optical disk having the thin transparent substrate thickness t1 becomes good, and the reproduction of the optical disk having the transparent substrate thickness t2 larger than that can be performed satisfactorily.

As in the first and second embodiments described above, if this embodiment is taken from another point of view, a plurality of divisions in which at least one surface is divided into a plurality of parts concentrically with the optical axis. In the objective lens 16 having a surface (three divided surfaces in the present embodiment), the light transmitted through the first divided surface Sd1 and the light transmitted through the third divided surface Sd3 have a predetermined thickness (first optical disk). ) Through the transparent substrate, the light is transmitted through the first divided surface Sd1 and passes through the transparent substrate, and the second divided light S2 near the optical axis side from the substantially central position of the second divided surface Sd2. The phase difference between the light passing through the dividing surface Sd2 and passing through the transparent substrate is set to (Δ1L) π (rad), and the light passing through the third dividing surface Sd3 and passing through the transparent substrate and the optical axis side from the center position Between the light passing through the second divided surface Sd2 on the opposite side to the light and passing through the transparent substrate. Let the phase difference be (Δ1H) π (ra
Assuming d), (Δ1H)> (Δ1L) is satisfied. In this case, similarly to the above, when t1> t2 and NA1> NA2, (Δ1H) <(Δ1L). Therefore,
(Δ1H) ≠ (Δ1L).

In other words, the second division plane S
The step amount of the second division surface Sd2 from the third division surface Sd3 is larger than the step amount of d2 from the first division surface Sd1. Also in this case, similarly to the above, t1> t2, NA1> N
In the case of A2, the third division surface at the boundary between the third division surface Sd3 and the second division surface Sd2 is obtained from the step amount from the first division surface Sd1 at the boundary between the first division surface Sd1 and the second division surface Sd2. The level difference from Sd3 is smaller. Further, at a predetermined position from the optical axis, the difference between the position of the surface interpolated from the first divided surface Sd1 and the third divided surface Sd3 and the position of the second divided surface Sd2 is substantially equal to the position of the second divided surface Sd2. Preferably, it is asymmetric about the center position.
Further, in this case, it is preferable that the difference increases as the distance from the optical axis increases.

As in the first and second embodiments described above, the division surfaces Sd1 to Sd3 are provided on the refraction surface S1 of the objective lens 16, the infinite system objective lens is used,
The provision of steps on the division surface, the number of division surfaces, and the surface shape of the second division surface are not limited to the contents described in the present embodiment.

In this embodiment, the first light source 111
The second light source 112 and the second light source 112 are synthesized by the synthesizing unit 19. However, the present invention is not limited thereto. In the optical pickup device shown in FIG.
12 may be switched.

In the present embodiment, when reproducing the first optical disk (ie, when passing through the transparent substrate having the thickness t1), the best wavefront due to the light beam passing through the first divided surface Sd1 and the third divided surface Sd3 is obtained. The aberration not only satisfies 0.05λrms (where λ (nm) is the wavelength of the light source used when reproducing the first optical disk), but also when reproducing the second optical disk (that is, the transparent film having the thickness t2). The best wavefront aberration due to the light beam passing through the first division surface Sd1 (when passing through the substrate) is 0.07λrms (where λ (nm) is the wavelength of the light source used when reproducing the second optical disk), which is the diffraction limit. By satisfying the condition, the reproduction signal of the second optical disc can be improved.

Incidentally, in the objective lens 16 in this embodiment, when the present applicant mistakenly used the optical pickup device shown in the first (or second) embodiment described above, the DVD was used as the first optical disk. Surprisingly, not only the reproduction but also the reproduction of the CD as the second optical disk by the light source of the same wavelength was possible. That is, the objective lens 16 of the present embodiment uses the light source of the wavelength λ1 to form the first optical information recording medium having a transparent substrate thickness t1 and the second optical information recording medium having a transparent substrate thickness t2 (where t2 ≠ t1). The light can be focused on the information recording surface of the two-optical information recording medium, and the wavelength λ
Even when a light source of 2 (where λ2 っ て も λ1) is used, light can be collected on the information recording surface of the second optical information recording medium. Thus, an optical pickup device for reproducing a DVD and a CD-R using two light sources having different wavelengths (corresponding to a light source of a wavelength of 610 nm to 670 nm for a DVD and a light source of a wavelength of 780 nm required for a CD-R) Lens and DVD and CD with one light source
Pickup device (wavelength 610 nm to 6
An objective lens used for a 70 nm light source) can be shared, and cost reduction accompanying mass production can be realized. It should be noted that such commonality is required to satisfy the conditions of NAL and NAH described in the first and second embodiments, even if the wavelength of the light source is changed from λ2 to λ1.

In this embodiment, since the first light source 111 and the second light source 112 are used at substantially the same magnification, one photodetector 30 can be used, and the configuration can be simplified. However, two photodetectors may be provided corresponding to the respective light sources 111 and 112, and the magnifications may be different.

(Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIG. 7 schematically showing the objective lens 16. FIG. 7A is a cross-sectional view of the objective lens 16, and FIG. 7B is a front view as viewed from the light source side. This embodiment is a modification of the objective lens 16 used in the optical pickup device described in the first to third embodiments described above, and is a modification of the objective lens described in the first to third embodiments. While the surface on the light source side of the lens 16 is a three-division refracting surface, the objective lens 16 of the present embodiment has a five-division refracting surface on the light source side. In addition,
This embodiment is divided into five parts, and the other parts are the same as the above-described first to third embodiments. Therefore, the description may be omitted.

In the present embodiment, the objective lens 16
Is a convex lens having a positive refractive power, both of the refracting surface S1 on the light source side and the refracting surface S2 on the optical disk 20 side having an aspherical shape. In addition, the refracting surface S of the objective lens 16 on the light source side
Reference numeral 1 denotes five first divisional surfaces Sd1 to fifth divisional surfaces Sd5 concentrically with the optical axis, that is, the first including the optical axis (in the vicinity of the optical axis).
The second divided surface Sd2... 2n + 1 (where n is a natural number and n = 2 in this embodiment) in the direction away from the optical axis from the divided surface (Sd1).
+1 plane). The boundaries between the divided surfaces Sd1 to Sd5 are provided with steps to form the respective divided surfaces Sd1 to Sd5. In this objective lens 16, the light beam (first light beam) passing through the first division surface Sd1 including the optical axis is the first light beam.
Used for reproducing information recorded on the optical disk and reproducing information recorded on the second optical disk, the second n-th divided surface Sd2
n (in the present embodiment, the light beam passing through the second divided surface Sd2 and the fourth divided surface Sd4) is mainly used for reproducing information recorded on the second optical disk, and is used for the second (n + 1) th divided surface Sd2n +
1 (in the present embodiment, the light beam passing through the third division surface Sd3 and the fifth division surface Sd5) has a shape mainly used for reproducing information recorded on the first optical disk.

As described above, in the present embodiment, by increasing the number of division surfaces, the second n-th division surface can be arranged on the high NA side. Instead, as the second optical disc, it is possible to reproduce an optical disc having a higher NA than that of the above-described first to third embodiments. In addition, the decrease in the amount of light during reproduction of the first optical disk due to the arrangement of the second n-th division surface on the high NA side can be compensated for by the second n-1 division surface (however, the first division surface does not matter). Not only the optical disc but also the second optical disc can be favorably reproduced.

Specifically, this objective lens 16 first
The first aspherical surface of the first refracting surface S1 and the second refracting surface S2 (the common refracting surface S2) such that the best wavefront aberration of the light beam focused on the first optical disk having the thickness of the transparent substrate t1 is 0.05 λrms or less. ) To design. Then, the amount of spherical aberration is smaller than the amount of spherical aberration generated when the thickness of the transparent substrate is converged on the second optical disk having the thickness t2 (t2 ≠ t1) via the lens having the first aspheric surface. The second aspherical surface of the first refraction surface is designed while keeping the second refraction surface S2 (common refraction surface) as it is. At this time, it is preferable that the paraxial radius of curvature of the second aspherical surface and the paraxial radius of curvature of the first aspherical surface be the same in order to perform good reproduction of the second optical disc that is reproduced in a defocused state. The second optical disc having the first aspherical surface has two positions near NAL-NAH near the required numerical aperture NA2.
Combine aspheric surfaces. The lens obtained in this manner becomes the objective lens 16 of the present embodiment.

In the case of combining, the second divided surface Sd2 and the fourth divided surface Sd4 are combined while being displaced in the optical axis direction, and the phase difference is used to reduce the amount of condensed light during reproduction of the first optical disk. Can be up. Further, although the second divided surface Sd2 and the fourth divided surface Sd4 are the same second aspheric surface, they may be different aspheric surfaces, and the amounts of shift in the optical axis direction may be changed. .

Here, the vicinity of NA2 at which the second aspheric surface is synthesized is 0.60 (NA2) <NA3 <1.3 (NA2).
(The lower limit of 0.60 (NA2) is practically 0.8
0 (NA2), more preferably 0.85 (NA2), and the upper limit of 1.3 (NA2).
Is practically preferably 1.1 (NA2). The upper limit of 1.3 (NA2) is set so that the wavelength of the light source when recording or reproducing the second optical disc information recording medium is 740 n.
1.1 (NA2) when m to 870 nm)
And 0.01 <NA4-NA3 <0.1
It is preferable that the numerical aperture NA3 and NA4 of the objective lens 16 on the optical disk side satisfy the condition of 2 (the upper limit of 0.12 is more preferably 0.1 in practical use).

In the case of this embodiment, as in the first embodiment, when reproducing a DVD having a thickness t1 of 0.6 mm of the transparent substrate as the first optical disc, the first
Division plane Sd1, third division plane Sd3, fifth division plane Sd5
Are formed at substantially the same first imaging position,
The wavefront aberration (the second divided surface Sd2 and the fourth divided surface Sd4
(Wavefront aberration excluding the light beam passing through) is 0.05λrm
s or less. Here, λ is the wavelength of the light source.

At this time, the light beam passing through the second divided surface Sd2 and the fourth divided surface Sd4 forms an image at a second image forming position different from the first image forming position. If the first image forming position is 0 (zero) and the objective lens 16 side is negative and the opposite side is positive, the second image forming position is -27 from the first image forming position.
The distance is set to be not less than μm and not more than −4 μm. In this embodiment, since t1 <t2 and NA1> NA2, the second
Although the imaging position is -27 μm to −4 μm from the first imaging position, if t1> t2 and NA1> NA2, the second imaging position is 4 μm to 27 μm from the first imaging position. That is, the absolute value of the distance between the first imaging position and the second imaging position is set to be in a range of 4 μm or more and 27 μm or less.

Further, when the objective lens 16 is viewed from the viewpoint of spherical aberration, a plurality of optical disks having different thicknesses of the transparent substrate can be reproduced by one condensing optical system at four opening positions near the numerical aperture NA2. Thus, the spherical aberration is configured to change discontinuously. As described above, the spherical aberration changes discontinuously (the direction of the change is the same as in the first to third embodiments), and from the viewpoint of the wavefront aberration, the spherical aberration near the numerical aperture NA2 is changed. The wavefront aberration becomes discontinuous at four places, and the slope of the wavefront aberration at each part of the discontinuity is:
The slopes of the curves connecting the ends of the curves on both sides of the discontinuous portion have different slopes.

The objective lens 16 of the present embodiment as described above
At the time of reproduction of the second optical disc (when passing through the transparent substrate having a thickness of t2), the spherical aberration between the numerical aperture NAL and the numerical aperture NAH is −2λ / (NA2) ² or more and 5λ / (NA).
2) ² satisfy the following conditions are preferred (however, λ in this case, is the wavelength of the light source used for reproducing the second optical disk). Further, this condition is 3 in the case of reproduction.
λ / (NA2) ² is preferably the following, or is preferably larger than 0 (zero) in consideration of recording (of course, reproduction is possible).

On the other hand, in the present embodiment, when viewed at the center position of the second n-th division surface (the second division surface Sd2 or the fourth division surface) in the direction orthogonal to the optical axis, the normal line of the second n-th division surface and the optical axis Is the angle formed by the (2n-1) -th divided plane (the first divided plane S
The angle between the optical axis and the normal line of the plane interpolated from d1 or the third division plane Sd3) and the (2n + 1) th division plane (the third division plane Sd3 or the fifth division plane Sd5). As a result, it is possible to satisfactorily reproduce both the first optical disk and the second optical disk. In the present embodiment, since t2> t1 and NA1> NA2, the angle between the normal line of the 2n-th divided surface and the optical axis is (2n−
1) Although the angle is larger than the angle between the normal line of the surface embedded from the division surface and the (2n + 1) th division surface and the optical axis, t2 <t
1. In the case of NA1> NA2, the value may be small.

Further, when viewed substantially at the center of a second n-th division plane (n is a natural number) which is the second division plane Sd2 or the fourth division plane Sd4 in a direction orthogonal to the optical axis, the 2n-th division plane The angle between the surface normal and the optical axis,
The angle between the optical axis and the normal of the surface (aspherical surface that has been fitted by the least squares method using the aspherical expression of Formula 1) interpolated from the (n-1) divided surface and the (2n + 1) th divided surface It is preferable to set the first divided surface Sd1 to the (2n + 1) th divided surface such that the difference between the first divided surface Sd1 and the second divided surface S2 is equal to or less than 0.02 °.

As in each of the above-described embodiments, when the present embodiment is taken from another viewpoint, a plurality of divided surfaces (at least one of the surfaces is divided concentrically with the optical axis). In the objective lens 16 having five divisional surfaces in the embodiment, the light transmitted through the (2n-1) th divisional surface on the optical axis side with respect to the 2nth divisional surface (where n is an integer of 1 or more) and the 2nth The second (2n +
1) When the light transmitted through the division surface has substantially the same phase through a transparent substrate having a predetermined thickness (first optical disc), the (2n-1) th division surface (for example, the first The light transmitted through the divisional surface Sd1 or the third divisional surface Sd3) through the transparent substrate and the light transmitted through the transparent substrate and the optical axis side of the second n-th divisional surface (for example, the second divisional surface Sd2 or the fourth divisional surface Sd4) substantially at the center position. 2n
Division surface (for example, the second division surface Sd2 or the fourth division surface Sd
4) and the phase difference between the light transmitted through the transparent substrate and (Δn)
L) π (for example, (Δ1L) π or (Δ2L) π) (r
ad), the light passing through the (2n + 1) -th divided surface (for example, the third divided surface Sd3 or the fifth divided surface Sd5) and passing through the transparent substrate, and the second light beam on the opposite side of the optical axis side from the center position.
Division surface (for example, the second division surface Sd2 or the fourth division surface Sd
4) and the phase difference between the light transmitted through the transparent substrate and (Δn)
H) π (eg, (Δ1H) π or (Δ2H) π) (r
ad), (ΔnH)> (ΔnL) is satisfied.
Also in this case, similarly to the above, t1> t2, NA1> NA2
In this case, (ΔnH) <(ΔnL). Therefore, (ΔnH) ≠ (ΔnL).

In other words, from another viewpoint, the (2n-1) -th division plane (for example, the first division plane Sd1 or the second division plane) of the 2n division plane (for example, the second division plane Sd2 or the fourth division plane Sd4). From the step amount from the three-divided surface Sd3), the second n-th divided surface (for example, the second divided surface Sd2 or the fourth divided surface difference Sd4) is obtained.
Is larger from the (2n + 1) th divided plane (for example, the third divided plane Sd3 or the fifth divided plane Sd5). In this case, similarly to the above, in the case of t1> t2 and NA1> NA2, from the (2n + 1) th plane of the 2nth division plane, the step amount of the 2nth division plane from the (2n-1) th plane is used. Is smaller. Further, at a predetermined position from the optical axis, the (2n-1) -th divided surface, the (2n + 1) -th divided surface (for example, the first divided surface Sd1 and the third divided surface Sd3)
Or the difference between the position of the surface interpolated from the third divided surface Sd3 and the fifth divided surface Sd5) and the position of the second n-th divided surface (for example, the second divided surface Sd2 or the fourth divided surface Sd4). Two division planes (for example, the second division plane Sd2 or the fourth division plane Sd
It is preferable that it is asymmetric about the center position of 4). Further, in this case, it is preferable that the difference increases as the distance from the optical axis increases.

In the present embodiment, the refracting surface S1 on the light source side of the objective lens 16 is divided into five parts. However, the present invention is not limited to this, and the refracting surface S1 is provided on an optical element of another condensing optical system (eg, a collimator lens). Alternatively, an optical element may be separately provided.

In this embodiment, the first division surface Sd
Although a step is provided at the boundary between the first to fifth division surfaces Sd5, a division surface may be formed continuously without providing a step at at least one boundary. Further, the boundary between the divided surfaces may be connected by, for example, a predetermined radius without bending. This R may be provided intentionally or may not be provided intentionally (as an example not provided intentionally, the objective lens 16 is formed of plastic or the like. In some cases, there is a boundary R formed in processing the mold).

In the present embodiment, when the objective lens 16 is viewed from the light source side, the second divided surface Sd2 and the fourth divided surface Sd4 are provided in a ring shape concentric with the optical axis. It is not limited, and may be provided in an interrupted ring shape. Also, the second
The division surface Sd2 and / or the fourth division surface Sd4 may be configured by a hologram or Fresnel. Note that the second division surface Sd2
Is composed of a hologram, one of the light beams divided into the zero-order light and the primary light is used for reproducing the first optical disk, and the other is used for reproducing the second optical disk. At this time, it is preferable that the light amount of the light beam used for reproducing the second optical disk is larger than the light amount of the light beam used for reproducing the first optical disk.

In the present embodiment, when reproducing the first optical disk (ie, when passing through the transparent substrate having the thickness t1), the best wavefront due to the light beam passing through the first divided surface Sd1 and the third divided surface Sd3 is obtained. The aberration not only satisfies 0.05λrms (where λ (nm) is the wavelength of the light source used when reproducing the first optical disk), but also when reproducing the second optical disk (that is, when the transparent substrate having the thickness t2 is used). The best wavefront aberration due to the light beam passing through the first split surface Sd1 is 0.07λrms (where λ is the diffraction limit).
By satisfying (nm) is the wavelength of the light source used when reproducing the second optical disk, it is possible to improve the reproduction signal of the second optical disk.

In the first to fourth embodiments described in detail above, the first divided surface is a surface including the optical axis. However, a surface in a very narrow area on the optical axis does not significantly affect light collection. Therefore, the surface of a very narrow region on the optical axis that does not affect such light collection may be flat, or may be a projection or a depression. The point is that a division surface used for reproducing the second optical disk may be provided near NA2, and the optical axis side (that is, near the optical axis) may be set as the first division surface.

In the above description, only the reproduction of the information recorded on the optical disk has been described. However, the information is recorded on the optical disk in that the light spot focused by the focusing optical system (objective lens) is important. The same applies to the case of performing the above operation, and it goes without saying that the above embodiment can be effectively used for recording.

Further, the first to fourth embodiments have an effect that the S-characteristic of the focus error signal is improved.

[0176]

In the following embodiments, the present invention is applied to a refracting surface on the light source side of the objective lens 16. Also,
DVD (transparent substrate thickness t1 =
0.6 mm, required numerical aperture NA1 = 0.60 (λ = 63
5 nm)) and a CD (transparent substrate thickness t2 = 1.2 mm, required numerical aperture NA2 = 0.
366 (λ = 635 nm) or NA2 = 0.45
(Λ = 780 nm)) or CD-R (transparent substrate thickness t2 = 1.2 mm, required numerical aperture NA2 = 0.50)
(Λ = 780 nm) (However, in the case of reproduction only, NA
2 = 0.45 (λ = 780 nm)). In the following example of the objective lens 16, the collimator lens 13 can make a substantially illuminated parallel light beam incident on the objective lens 16 by optimizing the design. Assuming that a collimator lens 13 capable of emitting a parallel light beam having an aberration is used, a configuration after the light beam enters the objective lens 16 will be described. The aperture disposed on the light source side of the objective lens 16 is defined as a first surface, and the radius of curvature of the i-th lens surface is ri in this order.
The distance from the second surface is di (for CD's, the value is changed to its value if described in di ', and the same as di when not described), the wavelength of the luminous flux of the laser light source at that interval Is represented by ni. When an aspherical surface is used for the optical surface, the expression is based on the above-described aspherical surface expression.

Tables 4, 7, 8, 11, 14, 15,
18, 19, 22, 23, 26, 27, 30, 31, 3,
In the descriptions in 4, 35, 38, and 39, the following is performed. Note that “n” in the following is a natural number.

First, the number in parentheses following NAL / NAH indicates the dividing plane (for example, NAL (2)
Indicates the value of NAL on the second division plane).

H2nmid indicates the height from the optical axis to the center of the second n-th divided surface in the direction orthogonal to the optical axis.

Further, θ2n-1,2n + 1, mid are as follows.
It shows the angle between the optical axis and the normal of the plane interpolated from the (2n-1) -th divided plane and the (2n + 1) -th divided plane at the height H2 nmid. Further, θ2n-1,2n +
1, mid, in detail, a plane obtained by extending the (2n-1) -th divided plane in the direction of the 2n-th divided plane is assumed, and a normal line and an optical axis at a height H2 nmid from the optical axis of the assumed plane. And the angle between the normal and the optical axis at a height H2 nmid from the optical axis on the assumed surface extending from the (2n + 1) th divided surface in the direction of the 2n divided surface. Mean angle. Here, when specifically assuming a surface, an aspherical expression shown in “Equation 1” may be referred to.

Further, θ2n, mid is the height H2nmi.
It shows the angle between d and the optical axis of the normal line of the 2n-th divided surface in d.

Δθ2n, mid is θ2n, mi
It shows the difference between d and θ2n-1,2n + 1, mid.

FIGS. 9, 13, 18, 22, 27, 3
The "defocus" described below (a) and (b) of 2, 37, 42, 47 and 52 is the information recording surface of the optical disk (when passing through a transparent substrate having a predetermined thickness and refractive index). The objective lens 16 is moved in the direction of the optical axis in order to obtain the best wavefront aberration when the traveling direction of the light beam from the light source is positive, centering on the position of the objective lens 16 that coincides with the geometric focal position. The amount (defocus amount) is shown.

Example 1 Example 1 is an objective lens 16 mounted on the one-light-source optical pickup device 10 of the second embodiment described above, and includes a first divided surface Sd1 to a third divided surface Sd3. This is an example in which the present invention is applied to an objective lens 16 having a step at the boundary of.

Tables 2 and 3 show the optical data of the objective lens.

[0186]

[Table 2]

[0187]

[Table 3]

In the objective lens of this embodiment, the position where the first aspherical surface intersects the optical axis and the position where the second aspherical surface intersects the optical axis are the same.

FIG. 8A shows the thickness t1 (= 0.6 m).
FIG. 8 (b) shows a spherical aberration diagram when the film passes through the transparent substrate of FIG.
mm) (FIG. 2) shows a spherical aberration diagram when the light passes through a transparent substrate (hereinafter, referred to as CD reproduction). Further, FIG.
FIG. 9B shows a wavefront aberration diagram when defocused at a position where the best wavefront aberration can be obtained during VD reproduction.
FIG. 9 shows a wavefront aberration diagram when viewed at a position where the best wavefront aberration at the time of D reproduction is obtained in a defocused state. Also,
Table 4 shows the numerical apertures of NAL and NAH, the amount of spherical aberration generated, the angle between the normal and the optical axis, the normal, and the values of each condition.

[0190]

[Table 4]

FIG. 10 is a graph showing the relative intensity distribution of the condensed spot when the best spot shape is obtained during DVD reproduction. FIG. 11 is a graph showing the relative intensity distribution when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

(Example 2) In Example 2, the two light sources of the third embodiment described above (wavelength λ1 of the first light source = 635) were used.
nm, the wavelength of the second light source λ2 = 780 nm), the objective lens 16 mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.

Tables 5 and 6 show the optical data of the objective lens.

[0194]

[Table 5]

[0195]

[Table 6]

In the objective lens of this embodiment, the position where the first aspherical surface intersects the optical axis and the position where the second aspherical surface intersects the optical axis are the same. Also, ni ′ in Table 5 is the second light source (λ
2 = 780 nm).

FIG. 12A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 12B shows a spherical aberration diagram at the time of reproducing a CD. FIG. 13A shows a wavefront aberration when defocused at a position where the best wavefront aberration can be obtained when reproducing a DVD, and FIG. 13B shows a position where the best wavefront aberration can be obtained when reproducing a CD. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. Table 7 shows NAL
And the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition.

[0198]

[Table 7]

FIG. 14 is a graph showing the relative intensity distribution of the converging spot when the best spot shape is obtained during DVD reproduction. FIG. 15 is a graph showing the relative intensity distribution when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

Further, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 16 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained at the time of CD reproduction at this time. In this case, NAL
Table 8 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition.

[0201]

[Table 8]

Example 3 Example 3 is an objective lens 16 mounted on the one-light-source optical pickup device 10 of the above-described second embodiment, and includes a second divided surface Sd2 and a third divided surface Sd3. This is an example in which the present invention is applied to the objective lens 16 in which a step is provided at the boundary between the objective lens 16 and a step is not provided at the boundary between the first divided surface Sd1 and the second divided surface Sd3.

Tables 9 and 10 show the optical data of the objective lens.

[0204]

[Table 9]

[0205]

[Table 10]

Note that “d2 =
"2.20702" means the distance between the intersection of the second aspherical surface (second divided surface) and the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical shape equation, on the optical axis. Represents.
That is, by setting this value, the first division surface and the second division surface
The divided surface is a continuous surface (having no step).

FIG. 17A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 17B shows a spherical aberration diagram at the time of reproducing a CD. FIG. 18A shows a wavefront aberration diagram when defocusing is performed on a position where the best wavefront aberration can be obtained during DVD reproduction, and FIG. 18B shows a position where the best wavefront aberration can be obtained during CD reproduction. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. Table 11 also shows that NA
The numerical values of L and NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0208]

[Table 11]

FIG. 19 shows a relative intensity distribution diagram of the condensed spot when the best spot shape is obtained at the time of reproducing a DVD, and FIG. 20 shows a distribution of the intensity at the time when the best spot shape is obtained at the time of reproducing the CD. 3 shows a relative intensity distribution diagram of a light spot.

Example 4 In Example 4, two light sources (wavelength λ1 = 635 of the first light source) of the third embodiment were used.
nm, the wavelength of the second light source λ2 = 780 nm), the objective lens 16 mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.

Tables 12 and 13 show the optical data of the objective lens.

[0212]

[Table 12]

[0213]

[Table 13]

[0214] In Table 13, "d2 =
2.996 ”means the distance on the optical axis between the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical shape equation. Represents. In this case, a phase difference is provided by shifting the second division surface by d2 in the optical axis direction, and the amount of condensed light (peak intensity) is increased. Also, ni ′ in Table 12 is the second light source (λ2 =
780 nm).

FIG. 21A shows a spherical aberration diagram when reproducing a DVD, and FIG. 21B shows a spherical aberration diagram when reproducing a CD. Further, FIG. 22A shows a wavefront aberration diagram when defocused to a position where the best wavefront aberration can be obtained at the time of reproducing a DVD, and FIG. 22B shows a position at which the best wavefront aberration can be obtained at the time of reproducing a CD. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. Also, Table 14 shows that NA
The numerical values of L and NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0216]

[Table 14]

FIG. 23 is a graph showing the relative intensity distribution of the condensed spot when the best spot shape is obtained during DVD reproduction. FIG. 24 is a graph showing the relative intensity distribution when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

Furthermore, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 25 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained at the time of reproducing the CD at this time. In this case, NAL
Table 15 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition.

[0219]

[Table 15]

Example 5 In Example 5, the two light sources (the wavelength λ1 of the first light source = 635) of the third embodiment described above were used.
nm, the wavelength of the second light source λ2 = 780 nm), the objective lens 16 mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.
In this embodiment, a CD is used as the second optical disc.
−R is assumed. Therefore, it is shown as NA2 = 0.5.

Tables 16 and 17 show the optical data of the objective lens.

[0222]

[Table 16]

[0223]

[Table 17]

In the objective lens of this embodiment, the position where the first aspherical surface intersects the optical axis and the position where the second aspherical surface intersects the optical axis are the same. Further, ni ′ in Table 16 indicates a refractive index at the second light source (λ2 = 780 nm).

FIG. 26A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 26B shows a spherical aberration diagram at the time of reproducing a CD-R. FIG. 27A shows a wavefront aberration diagram when defocused at a position where the best wavefront aberration can be obtained during DVD reproduction, and FIG. 27B shows the best wavefront aberration during CD-R reproduction. FIG. 3 shows a wavefront aberration diagram when the image is defocused at a position where the image is defocused. Table 18 shows the numerical apertures of NAL and NAH, the amount of spherical aberration generated,
The angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0226]

[Table 18]

FIG. 28 is a diagram showing the relative intensity distribution of the converging spot when the best spot shape is obtained during DVD reproduction. FIG. 29 is a diagram showing the case where the best spot shape is obtained during CD-R reproduction. 3 shows a relative intensity distribution diagram of the focused spot of FIG.

Further, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 30 shows a relative intensity distribution diagram of the condensed spot when the best spot shape is obtained at the time of reproducing the CD at this time. In this case, NAL
Table 19 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal and the optical axis, the normal, and the value of each condition.

[0229]

[Table 19]

Example 6 In Example 6, the two light sources (wavelength λ1 = 635 of the first light source) of the third embodiment described above were used.
nm, the wavelength of the second light source λ2 = 780 nm), and the objective lens 16 mounted on the optical pickup device 10 using the objective lens 16 described in the fourth embodiment.
That is, this is an example in which the objective lens 16 having a step at the boundary between the first divided surface Sd1 to the fifth divided surface Sd5 is mounted. In this embodiment, the second optical disc is a CD-ROM.
R is assumed. Therefore, NA2 = 0.5
As shown.

Tables 20 and 21 show the optical data of the objective lens.

[0232]

[Table 20]

[0233]

[Table 21]

In the objective lens of this embodiment, the first aspherical surface (the surface of the first divided surface Sd1, the third divided surface Sd3, and the fifth divided surface Sd5 (or a surface obtained by extending this surface) is the optical axis. The intersection position is the same as the position where the surfaces obtained by extending the respective division surfaces of the second division surface Sd2 and the fourth division surface Sd4 (both combine the second aspheric surface) intersect the optical axis.
Indicates the refractive index at the second light source (λ2 = 780 nm).

FIG. 31 (a) shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 31 (b) shows a spherical aberration diagram at the time of reproducing a CD-R. FIG. 32A shows a wavefront aberration diagram when defocused at a position where the best wavefront aberration can be obtained during DVD reproduction, and FIG. 32B shows the best wavefront aberration during CD-R reproduction. FIG. 3 shows a wavefront aberration diagram when the image is defocused at a position where the image is defocused. Table 22 also shows the numerical apertures of NAL and NAH, the amount of spherical aberration generated,
The angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0236]

[Table 22]

FIG. 33 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained during DVD reproduction. FIG. 34 shows a case where the best spot shape is obtained during CD-R reproduction. 3 shows a relative intensity distribution diagram of the focused spot of FIG.

Further, the objective lens of this embodiment is:
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 35 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained at the time of reproducing the CD at this time. In this case, NAL
Table 23 shows the numerical aperture of NAH, the amount of generation of spherical aberration, the angle between the normal and the optical axis, the normal, and the value of each condition.

[0239]

[Table 23]

(Example 7) In Example 7, the two light sources (the wavelength λ1 of the first light source = 635) of the third embodiment were used.
nm, the wavelength of the second light source λ2 = 780 nm), and the objective lens 16 mounted on the optical pickup device 10 using the objective lens 16 described in the fourth embodiment.
That is, this is an example in which the objective lens 16 having a step at the boundary between the first divided surface Sd1 to the fifth divided surface Sd5 is mounted. In this embodiment, the second optical disc is a CD-ROM.
R is assumed. Therefore, NA2 = 0.5
As shown.

Tables 24 and 25 show the optical data of the objective lens.

[0242]

[Table 24]

[0243]

[Table 25]

Note that “d2 =
2.996 ”and“ d4 = 2.2003 ”mean the optical axis when the shapes of the second divided surface and the fourth divided surface (both are the second aspheric surfaces) are extended to the optical axis in accordance with the aspheric shape formula. And the distance on the optical axis between the intersection of the third surface and the third surface. This means that the second division plane is shifted by d2 in the optical axis direction, and
A phase difference is provided by shifting the fourth division surface by d4 in the optical axis direction to increase the amount of condensed light (peak intensity). Also, ni ′ in Table 24 is the second light source (λ2 = 78).
0 nm).

FIG. 36 (a) shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 36 (b) shows a spherical aberration diagram at the time of reproducing a CD-R. FIG. 37 (a) shows a wavefront aberration diagram when defocused at a position where the best wavefront aberration can be obtained during DVD reproduction, and FIG. 37 (b) shows the best wavefront aberration during CD-R reproduction. FIG. 3 shows a wavefront aberration diagram when the image is defocused at a position where the image is defocused. Table 26 shows the numerical apertures of NAL and NAH, the amount of spherical aberration generated,
The angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0246]

[Table 26]

FIG. 38 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained during DVD reproduction. FIG. 39 shows a case where the best spot shape is obtained during CD-R reproduction. 3 shows a relative intensity distribution diagram of the focused spot of FIG.

Further, the objective lens of this embodiment is:
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 40 shows a relative intensity distribution diagram of the condensed spot when the best spot shape is obtained at the time of CD reproduction at this time. In this case, NAL
Table 27 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal and the optical axis, the normal, and the value of each condition.

[0249]

[Table 27]

(Eighth Embodiment) In the eighth embodiment, the two light sources (wavelength λ1 = 635 of the first light source) of the third embodiment described above are used.
nm, the wavelength of the second light source λ2 = 780 nm), the objective lens 16 mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.

Tables 28 and 29 show the optical data of the objective lens.

[0252]

[Table 28]

[0253]

[Table 29]

In Table 29, “d2 =
2.1995 ”means the distance on the optical axis between the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical shape equation. Represents. Also, ni ′ in Table 28 is the second light source (λ2 = 780 nm)
Shows the refractive index at.

FIG. 41 (a) shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 41 (b) shows a spherical aberration diagram at the time of reproducing a CD. FIG. 42A shows a wavefront aberration diagram when defocused at a position where the best wavefront aberration can be obtained at the time of reproducing the DVD, and FIG. 42B shows a position at which the best wavefront aberration can be obtained at the time of reproducing the CD. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. In Table 30, NA
The numerical values of L and NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0256]

[Table 30]

FIG. 43 is a graph showing the relative intensity distribution of the condensed spot when the best spot shape is obtained during DVD reproduction, and FIG. 44 is a graph showing the relative intensity distribution when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

Further, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 45 shows a relative intensity distribution diagram of the converged spot when the best spot shape is obtained at the time of reproducing the CD at this time. In this case, NAL
Table 31 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal and the optical axis, the normal, and the value of each condition.

[0259]

[Table 31]

(Embodiment 9) In the ninth embodiment, the two light sources (wavelength λ1 = 635 of the first light source) of the third embodiment described above are used.
nm, the wavelength of the second light source λ2 = 780 nm), the objective lens 16 mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.

Tables 32 and 33 show the optical data of the objective lens.

[0262]

[Table 32]

[0263]

[Table 33]

[0264] Note that "d2 =
2.200 ”means the distance between the intersection with the optical axis when the shape of the second aspherical surface (second division surface) is extended to the optical axis according to the aspherical shape formula, and the distance on the optical axis with the third surface. Represents. Also,
Ni ′ in Table 32 indicates the refractive index at the second light source (λ2 = 780 nm).

FIG. 46A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 46B shows a spherical aberration diagram at the time of reproducing a CD. Further, FIG. 47A shows a wavefront aberration diagram when defocusing is performed on a position where the best wavefront aberration can be obtained when reproducing a DVD, and FIG. 47B shows a position where the best wavefront aberration can be obtained when reproducing a CD. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. In Table 34, NA
The numerical values of L and NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0266]

[Table 34]

FIG. 48 is a graph showing the relative intensity distribution of the converging spot when the best spot shape is obtained during DVD reproduction. FIG. 49 is a diagram showing the relative intensity distribution when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

Further, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 50 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained at the time of CD reproduction at this time. In this case, NAL
Table 35 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition.

[0269]

[Table 35]

Example 10 In Example 10, the two light sources of the third embodiment described above (wavelength λ1 of the first light source = 6) were used.
(35 nm, wavelength λ2 of the second light source = 780 nm), the objective lens 16 to be mounted on the optical pickup device 10 and having a step at the boundary between the first divided surface Sd1 and the third divided surface Sd3. It is an example to which the present invention is applied.

Tables 36 and 37 show the optical data of the objective lens.

[0272]

[Table 36]

[0273]

[Table 37]

[0274] In Table 37, "d2 =
2.1995 ”means the distance on the optical axis between the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical shape equation. Represents. Also, ni ′ in Table 36 is the second light source (λ2 = 780 nm)
Shows the refractive index at.

FIG. 51 (a) shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 51 (b) shows a spherical aberration diagram at the time of reproducing a CD. FIG. 52A shows a wavefront aberration diagram when defocusing is performed on a position where the best wavefront aberration can be obtained when reproducing a DVD, and FIG. 52B shows a position where the best wavefront aberration can be obtained when reproducing a CD. FIG. 4 shows a wavefront aberration diagram when viewed in a defocused state. In Table 38, the NA
The numerical values of L and NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition are shown.

[0276]

[Table 38]

FIG. 53 shows a relative intensity distribution diagram of the condensed spot when the best spot shape is obtained during DVD reproduction. FIG. 54 shows a collection when the best spot shape is obtained during CD reproduction. 3 shows a relative intensity distribution diagram of a light spot.

Further, the objective lens of this embodiment is
Even when mounted on the optical pickup device 10 using one light source (light source wavelength λ1 = 635 nm), not only DVD but also CD could be reproduced. FIG. 55 shows a relative intensity distribution diagram of the converging spot when the best spot shape is obtained at the time of reproducing the CD at this time. In this case, NAL
Table 39 shows the numerical aperture of NAH, the amount of spherical aberration generated, the angle between the normal line and the optical axis, the normal line, and the value of each condition.

[0279]

[Table 39]

As described above, according to Examples 1 to 10, two optical discs having different thicknesses of the transparent substrate were successfully reproduced with one condensing optical system (of which one objective lens). There is no problem in recording. In particular, in the second and fourth to tenth embodiments, along with the reproduction of the DVD as the first optical disk using the two light sources,
Reproduction of CD-R as second optical disk (wavelength of light source is 7
80 nm is essential). Further, in the second and fourth to tenth embodiments, the DVD
In addition, reproduction of CDs was also successfully performed. Further, Example 5
7, the required numerical aperture for the second optical disc is NA
= 0.5 and could be used sufficiently for CD-R recording.

Also, of the first to tenth embodiments, the first embodiment,
In 3, 8 to 10, the thickness of the transparent substrate is 1.2 mm
The reproduction signal of the second optical disk was particularly good. This is because, as shown in Table 40, Examples 1, 3, 8 to 10
In (2), the best wavefront aberration (referred to as the amount of wavefront aberration in the first divided plane) due to the light beam passing through the first divided plane satisfies the diffraction-limited performance of 0.07λ.

[0282]

[Table 40]

[0283] In Table 40, the upper table shows the first split plane in-plane wavefront aberration amount in the case of reproducing the second optical disk having the wavelength λ of the light source of 635 nm and the thickness of the transparent substrate of 1.2 mm. However, since Examples 2 and 4 to 10 are examples using two light sources, the lower table shows a case where the second optical disk having a wavelength λ of the light sources of 780 nm and a transparent substrate thickness of 1.2 mm is reproduced. The first divided in-plane wavefront aberration amount is shown.

[0284] In Examples 1 to 10 described above,
If n is a natural number, the (2n-1) -th divided plane (for example,
The light passing through the first divided surface Sd1 or the third divided surface and passing through the transparent substrate of the DVD and the optical axis from the substantially center position of the 2n divided surface (for example, the second divided surface Sd2 or the fourth divided surface Sd4). (ΔnL) π (for example, (Δ1L)) which is the phase difference between the light passing through the second n-th division surface (for example, the second division surface Sd2 or the fourth division surface Sd4) and passing through the transparent substrate of the DVD.
π or (Δ2L) π) (rad) and (2n +
1) The light passing through the division surface (for example, the third division surface Sd3 or the fifth division surface Sd5) and passing through the transparent substrate of the DVD, and the second n-th division surface (for example, opposite to the optical axis side from the center position) (Δn) with the light transmitted through the second divided surface Sd2 or the fourth divided surface Sd4) and transmitted through the transparent substrate of the DVD.
H) π (eg, (Δ1H) π or (Δ2H) π) (r
ad) are shown in Table 41. In this case, the sign of the phase difference is such that the traveling direction of the light (the direction toward the optical disk) is positive and the (2n-1) th divided plane or the (2n + 1) th
The phase difference between the light transmitted through the divided surface and transmitted through the transparent substrate of the DVD and the light transmitted through the second n divided surface and transmitted through the transparent substrate of the DVD is compared.

[0285]

[Table 41]

As is clear from this table, Examples 1 to 1
In all 0, (ΔnH)> (ΔnL) is satisfied. Note that the values in Table 41 are the values of each of the divided surfaces Sd1 to Sd.
3 shows a phase difference in a light beam incident on each division surface at a boundary between 3 (or Sd5).

[0287]

As described in detail above, in the present invention, recording / recording of a plurality of optical information recording media by one condensing optical system is performed.
It can be reproduced, can be realized at low cost and without complexity, and can also be applied to an optical information recording medium with a high NA. Further, according to the present invention, recording / reproducing of a plurality of optical information recording media can be performed by one condensing optical system by positively utilizing generation of spherical aberration.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device.

FIGS. 2A and 2B are a cross-sectional view schematically showing an objective lens and a front view as viewed from a light source side.

FIG. 3 is a cross-sectional view schematically showing an objective lens.

FIG. 4 is a diagram schematically showing a spherical aberration diagram of an objective lens.

FIG. 5 is a diagram schematically showing a wavefront aberration diagram of an objective lens.

FIG. 6 is a schematic configuration diagram of an optical pickup device according to a third embodiment.

FIGS. 7A and 7B are a sectional view schematically showing an objective lens according to a fourth embodiment and a front view as viewed from a light source side;

FIG. 8 is an aberration diagram of the objective lens according to the first embodiment.

FIG. 9 is a wavefront aberration diagram when the objective lens in Example 1 is defocused to a position where the best wavefront aberration is obtained.

FIG. 10 is a relative intensity distribution diagram of a condensed spot when the best spot shape at the time of reproducing a DVD is obtained by the objective lens of Example 1.

FIG. 11 shows a relative intensity distribution diagram of a converging spot when the best spot shape is obtained during CD reproduction according to the first embodiment.

FIG. 12 is an aberration diagram of the objective lens of the second embodiment.

FIG. 13 is a wavefront aberration diagram when the objective lens in Example 2 is defocused to a position where the best wavefront aberration is obtained.

FIG. 14 is a relative intensity distribution diagram of a condensed spot when the best spot shape during DVD reproduction is obtained by the objective lens of Example 2.

FIG. 15 shows a relative intensity distribution diagram of a converging spot when the best spot shape is obtained during CD reproduction according to the second embodiment.

FIG. 16 shows a graph of C at a wavelength of 635 nm with the objective lens of Example 2.
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 17 is an aberration diagram of the objective lens of the third embodiment.

FIG. 18 is a wavefront aberration diagram when the objective lens of Example 3 is defocused to a position where the best wavefront aberration is obtained.

FIG. 19 is a relative intensity distribution diagram of a condensed spot when the best spot shape during DVD reproduction is obtained with the objective lens of Example 3.

FIG. 20 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD reproduction according to the third embodiment.

FIG. 21 is an aberration diagram of the objective lens in the fourth embodiment.

FIG. 22 is a wavefront aberration diagram when the objective lens of Example 4 is defocused to a position where the best wavefront aberration is obtained.

FIG. 23 is a relative intensity distribution diagram of a converging spot when the best spot shape at the time of reproducing a DVD is obtained by the objective lens of Example 4.

FIG. 24 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD reproduction in Example 4.

FIG. 25 shows C at a wavelength of 635 nm using the objective lens of Example 4.
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 26 is an aberration diagram of the objective lens of the fifth embodiment.

FIG. 27 is a wavefront aberration diagram when the objective lens of Example 5 is defocused to a position where the best wavefront aberration is obtained.

FIG. 28 is a relative intensity distribution diagram of a converged spot when the best spot shape at the time of DVD reproduction is obtained by the objective lens of Example 5;

FIG. 29 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD-R reproduction in Example 5.

FIG. 30 shows a graph of C at a wavelength of 635 nm with the objective lens of Example 5.
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 31 is an aberration diagram of the objective lens of the sixth embodiment.

FIG. 32 is a wavefront aberration diagram when the objective lens of Example 6 is defocused to a position where the best wavefront aberration is obtained.

FIG. 33 is a diagram showing a relative intensity distribution of a condensed spot when the best spot shape during DVD reproduction is obtained by the objective lens of Example 6;

FIG. 34 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD-R reproduction in Example 6.

FIG. 35 shows C at a wavelength of 635 nm with the objective lens of Example 6;
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 36 is an aberration diagram of the objective lens of the seventh embodiment.

FIG. 37 is a wavefront aberration diagram when the objective lens of Example 7 is defocused to a position where the best wavefront aberration is obtained.

FIG. 38 is a relative intensity distribution diagram of a condensed spot when the best spot shape during DVD reproduction is obtained by the objective lens of Example 7;

FIG. 39 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD-R reproduction in Example 7.

FIG. 40 shows C at a wavelength of 635 nm using the objective lens of Example 7.
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 41 is an aberration diagram of the objective lens in the eighth embodiment.

FIG. 42 is a wavefront aberration diagram when the objective lens in Example 8 is defocused to a position where the best wavefront aberration is obtained.

FIG. 43 is a diagram showing a relative intensity distribution of a condensed spot when the best spot shape at the time of reproducing a DVD is obtained by the objective lens of Example 8;

FIG. 44 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD reproduction in Example 8.

FIG. 45: C at a wavelength of 635 nm with the objective lens of Example 8
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 46 is an aberration diagram of the objective lens in the ninth embodiment.

FIG. 47 is a wavefront aberration diagram when the objective lens of Example 9 is defocused to a position where the best wavefront aberration is obtained.

FIG. 48 is a diagram showing a relative intensity distribution of a condensed spot when the best spot shape at the time of reproducing a DVD is obtained by the objective lens of Example 9;

FIG. 49 is a diagram showing a relative intensity distribution diagram of a converged spot when the best spot shape is obtained at the time of reproducing a CD according to the ninth embodiment.

FIG. 50 shows a graph of C at the wavelength of 635 nm with the objective lens of Example 9.
FIG. 9 shows a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during D reproduction.

FIG. 51 is an aberration diagram of the objective lens of the tenth embodiment.

FIG. 52 is a wavefront aberration diagram when the objective lens of Example 10 is defocused to a position where the best wavefront aberration is obtained.

FIG. 53 is a diagram showing a relative intensity distribution of a light-converged spot when the best spot shape at the time of reproducing a DVD is obtained by the objective lens of Example 10;

FIG. 54 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained during CD reproduction in Example 10.

FIG. 55 shows a relative intensity distribution diagram of a condensed spot when the best spot shape is obtained at the time of CD reproduction at a wavelength of 635 nm with the objective lens of Example 10.

[Explanation of symbols]

 Reference Signs List 10 optical pickup device 11 semiconductor laser (light source) 13 collimator lens 16 objective lens 17 aperture 20 optical information recording medium (optical disk) 21 transparent substrate 22 information recording surface S1, S2 refraction surface Sd1-Sd5 division surface 111 first light source (first) (Second semiconductor laser) 112 Second light source (second semiconductor laser)

Claims (24)

[Claims] 1. A light source emits light to a first optical information recording medium having a transparent substrate thickness of t1 and a second optical information recording medium having a transparent substrate thickness of t2 (where t2 ≠ t1). In a recording / reproducing method for an optical information recording medium, a light beam is condensed on an information recording surface via a transparent substrate by one condensing optical system, and information is recorded on the information recording surface or information is reproduced on the information recording surface. The first light beam near the optical axis is used for recording or reproduction of the first optical information recording medium and the recording or reproduction of the second optical information recording medium, and the second light beam outside the first light beam is mainly the second light beam. A third light beam outside the second light beam is used mainly for recording or reproduction on the first optical information recording medium, and is used for recording or reproduction on the optical information recording medium. Playback method. 2. A light source emits light to a first optical information recording medium having a transparent substrate thickness of t1 and a second optical information recording medium having a transparent substrate thickness of t2 (where t2 （t1). An optical pickup device for condensing a light beam on an information recording surface via a transparent substrate with one condensing optical system and recording information on the information recording surface or reproducing information on the information recording surface, wherein the condensing optical system Utilizes a first light flux near the optical axis for recording or reproduction on a first optical information recording medium and recording or reproduction on a second optical information recording medium, and mainly uses a second light flux outside the first light flux as a second light flux. An optical pickup device used for reproducing an optical information recording medium and having a function of mainly using a third light beam outside the second light beam for recording or reproducing on the first optical information recording medium. 3. An optical pickup device which focuses a light beam from a light source on an information recording surface of an optical information recording medium and records information on the information recording surface or reproduces information recorded on the information recording surface. Positioning at least one optical surface of the condensing optical system between a first division surface located at the center of the optical surface near the optical axis and the second division surface with the second division surface interposed therebetween When recording or reproducing information on the first optical information recording medium having a transparent substrate having a thickness of t1, the first divided surface and the third divided surface are mainly used. A beam spot is formed by the light beam passing through the surface, and when recording or reproducing on the second optical information recording medium having a transparent substrate having a thickness of t2 (where t2 ≠ t1), the first
An optical pickup device, wherein a beam spot is formed by a light beam having passed through a division surface and a second division surface. 4. A plurality of divided surfaces, at least one of which is divided concentrically with the optical axis, a first divided surface near the optical axis, and a third divided surface outside the first divided surface. When the light beam passing through is measured to form an image at substantially the same first imaging position, the first imaging position and the second division surface between the first division surface and the third division surface are measured. An objective lens, wherein an absolute value of a distance from a second imaging position at which a passing light beam forms an image is 4 μm or more and 40 μm or less. 5. A first divided surface having at least one surface divided into a plurality of portions concentrically with the optical axis, a first divided surface near the optical axis, and a third divided surface outside the first divided surface. When the light beam passing through is measured so as to form an image at substantially the same first imaging position, the light beam passing through the second division surface between the first division surface and the third division surface is imaged. 2. An objective lens wherein the image forming position is closer to the objective lens than the first image forming position. 6. The objective lens according to claim 5, wherein a distance between the first position and the second position is −40 μm or more and −4 μm or less. 7. When a plurality of divided surfaces having at least one surface divided into a plurality of portions concentrically with an optical axis and a predetermined incident light beam passes through a transparent substrate having a predetermined thickness,
Of the luminous flux passing through the first division plane including the optical axis, the position where the light ray passing near the optical axis intersects the optical axis and the light ray passing through the end of the first division plane in a direction orthogonal to the optical axis are Between the position intersecting with the optical axis, the light beam passing through the second division surface outside the first division surface intersects the optical axis, and the light beam passing through the third division surface outside the second division surface is A light beam passing near the optical axis intersects the optical axis at a position farther from a position where the light beam passing through the end of the first split surface intersects the optical axis with respect to a position intersecting the optical axis. Objective lens. 8. A light beam emitted from a light source is condensed as a light spot on an information recording surface of the optical information recording medium by a condensing optical system via a transparent substrate of the optical information recording medium, and information is recorded on the information recording surface. In an optical pickup device for recording or reproducing information recorded on an information recording surface, the light of the condensing optical system necessary for recording or reproducing the first optical information recording medium having a transparent substrate having a thickness of t1. The necessary numerical aperture on the information recording medium side is NA1, and the optical information recording of the condensing optical system necessary for recording or reproducing on the second optical information recording medium having a thickness of the transparent substrate of t2 (where t2 ≠ t1). Assuming that the required numerical aperture on the medium side is NA2 (where NA2 <NA1), the condensing optical system has a numerical aperture of at least 2 near NA2.
An optical pickup device having a function of changing spherical aberration discontinuously at one opening position. 9. A light beam from a light source is condensed as a light spot on an information recording surface of an optical information recording medium via a transparent substrate of the optical information recording medium to record information on the optical information recording medium or An objective lens of a pickup device for reproducing information recorded on a recording medium, wherein the wavelength of the light source is λ, and the thickness of the transparent substrate is t1, and the objective lens is necessary for recording or reproducing on the first optical information recording medium. The required numerical aperture on the optical information recording medium side is NA1, the optical information recording of the objective lens necessary for recording or reproducing on the second optical information recording medium having a transparent substrate thickness of t2 (where t2 ≠ t1). An optical pickup device characterized in that when the required numerical aperture on the medium side is NA2 (where NA2 <NA1), the spherical aberration changes discontinuously at at least two aperture positions near NA2. Of the objective lens. 10. The minimum numerical aperture of the at least two aperture positions is NAL, and the maximum numerical aperture is N.
When the numerical aperture NAL and the numerical aperture NAL in the direction orthogonal to the optical axis and viewed at the approximate center of the numerical aperture NAH, the numerical aperture NAL
The angle between the normal to the optical axis and the optical axis is the angle between the normal to the optical axis from the optical axis to the numerical aperture NAL and the normal to the plane interpolated from the numerical aperture NAH to the numerical aperture NA1 Than,
The objective lens of the optical pickup device according to claim 9, wherein the value is large when t2> t1 and small when t2 <t1. 11. A method of designing an objective lens for condensing a light beam emitted from a light source having a wavelength λ on a plurality of optical information recording media having different thicknesses of a transparent substrate, the first light having a thickness of t1 of the transparent substrate. Numerical aperture N of the objective lens on the optical information recording medium side required for recording or reproduction of the information recording medium
Within the range of A1, the first aspherical surface and the common refraction surface are adjusted so that the best wavefront aberration of the light beam condensed on the first optical information recording medium via the transparent substrate having the thickness t1 is 0.05λrms or less. In addition to the design, the amount of spherical aberration generated in the light beam focused on the second optical information recording medium having the thickness of the transparent substrate t2 (where t2 ≠ t1) is
The second aspherical surface with respect to the common refracting surface is designed so that the amount of spherical aberration generated when the light is condensed on the second optical information recording medium via the first aspherical surface is reduced. And the second aspherical surface, where the numerical aperture on the information recording surface side of the objective lens required for recording or reproducing the second optical information recording medium is NA2 (where NA2 <NA1), A design method of the objective lens, wherein the second aspherical surface is combined so that the second aspheric surface is located at a portion where the light flux near the NA2 passes. 12. The method for designing an objective lens according to claim 11, wherein an on-axis radius of curvature of the first aspheric surface and an on-axis radius of curvature of the second aspheric surface are the same. 13. The first aspherical surface passes through a first aspherical surface located closer to the optical axis than the second aspherical surface to be synthesized, and is collected on a second optical information recording medium having a transparent substrate having a thickness of t2. 13. The method of designing an objective lens according to claim 11, wherein the design is performed such that the best wavefront aberration of the emitted light beam is 0.07 [lambda] rms or less. 14. An objective lens for converging a light beam emitted from a light source on a plurality of optical information recording media having different thicknesses of a transparent substrate, wherein at least one refracting surface of the objective lens has a thickness of the transparent substrate. Numerical aperture N on the optical information recording medium side of the objective lens required for recording or reproduction of the first optical information recording medium at t1
Within the range of A1, the first aspherical surface such that the best wavefront aberration of the light beam condensed through the transparent substrate having the thickness t1 is 0.05λrms or less, and the thickness of the transparent substrate is t2 (where t2 The amount of spherical aberration of the light beam focused on the second optical information recording medium of (t1) is
A second aspherical surface that is smaller than the amount of spherical aberration generated when the light is condensed on the second optical information recording medium via the first aspherical surface is recorded on the second optical information recording medium. The numerical aperture on the information recording surface side of the objective lens required for reproduction is NA2
(Where NA2 <NA1), wherein the first aspherical surface is constituted by a refraction surface synthesized such that the second aspherical surface is located at a portion through which a light beam near the NA2 passes. lens. 15. A light beam emitted from a light source is condensed on an information recording surface via a transparent substrate by a condensing optical system on a first optical information recording medium having a transparent substrate having a thickness of t1, and an information recording surface is provided. An optical pickup device for recording information thereon or reproducing information on an information recording surface, comprising: a necessary aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the first optical information recording medium. Number is NA
1. The light condensing necessary for recording or reproducing a second optical information recording medium having a transparent substrate thickness t2 (t2 ≠ t1) different from the transparent substrate thickness t1 of the first optical information recording medium. The required numerical aperture of the optical system on the optical information recording medium side is NA2 (however,
When NA2 <NA1 is satisfied, 0.60 (NA2) <NA3 <1.3 (NA2) (where the wavelength of the light source for recording or reproducing the second optical information recording medium is 740 nm). In the case of ８870 nm, the upper limit of this expression is 1.1 (NA2). The numerical aperture NA3 on the optical information recording medium side of the condensing optical system that satisfies the condition of 0.01 <NA4-NA3 <0.12. Acting on a light beam passing between the first optical information recording medium and the numerical aperture NA4, the surface of the second optical information recording medium is mainly used for recording or reproduction, so that the thicknesses of the transparent substrates are different from each other. For the first optical information recording medium and the second optical information recording medium, the same condensing optical system
An optical pickup device for performing recording or reproduction. 16. The second image forming position of the second light beam that has passed through a surface mainly used for recording or reproduction of the second optical information recording medium is a first light beam inside the second light beam. And the second
When measured so that a third light beam outside the light beam forms an image at substantially the same first image forming position, the absolute value of the distance from the first image forming position is 4 μm or more and 40 μm or less. The optical pickup device according to claim 15, wherein: 17. A first optical information recording medium having a transparent substrate having a thickness of t1 and a thickness of a transparent substrate having a thickness of t2 (where t2 ≠ t1).
The second optical information recording medium, the light flux emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system, and the information is recorded on the information recording surface or the information recording surface is recorded. In an optical pickup device for recording / reproducing an optical information recording medium for reproducing the above information, a necessary aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the first optical information recording medium. The numerical aperture is NA1, and the required numerical aperture of the condensing optical system on the optical information recording medium side required for recording or reproducing the second optical information recording medium is NA2.
(Where NA2 <NA1) When the condensing optical system is configured to obtain the best wavefront aberration within the range of numerical aperture NA1 when passing through a transparent substrate having a thickness t1 at a predetermined magnification. An optical pickup device characterized in that the wavefront aberration is discontinuous in at least two places near the numerical aperture NA2 when viewed on a wavefront aberration curve with the wavefront aberration on the vertical axis and the numerical aperture on the horizontal axis. 18. A first optical information recording medium having a transparent substrate having a thickness of t1 and a thickness of a transparent substrate having a thickness of t2 (where t2 ≠ t1).
The second optical information recording medium, the light flux emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system, and the information is recorded on the information recording surface or the information recording surface is recorded. An objective lens of an optical pickup device for recording / reproducing an optical information recording medium for reproducing the above information, wherein the objective lens has at least one surface near a first optical axis.
The first light flux passing through the first divided surface is divided into a second optical information recording medium and a second optical information recording device, wherein the first light flux passing through the first divided surface is divided into a second (n + 1) th (where n is a natural number) divided surface. The light beam passing through the even-numbered division surface is mainly used for recording or reproduction of the second optical information recording medium while the light beam passing through the odd-numbered division surface excluding the first division surface is mainly used for recording or reproduction of the medium. First
An objective lens of an optical pickup device, which is used for recording or reproduction of an optical information recording medium. 19. A light beam having a wavelength λ having a uniform phase from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, and information is recorded or recorded on the information recording surface. In an optical pickup device for reproducing information recorded on an information recording surface, a light flux from the light source is supplied to the condensing optical system to have a thickness t1,
The light is condensed through a parallel plane plate having a refractive index of n1, and within a range of the first numerical aperture on the side of the parallel plane plate, a wavefront aberration curve obtained by measuring the wavefront aberration in a state where the wavefront aberration is optimal is as follows: In a range of a second numerical aperture smaller than the first numerical aperture on the parallel plane plate side of the converging optical system, the converging optical system has a portion where the wavefront aberration is discontinuous, and At least one refraction of the condensing optical system is such that the slope of the wavefront aberration is a slope different from the slope of a straight line connecting the ends of the curves on both sides of the discontinuous portion. An optical pickup device, wherein a surface is constituted by a plurality of divided surfaces concentrically with an optical axis. 20. A method for recording information on an optical information recording medium or reproducing information recorded on the optical information recording medium, the method comprising the steps of: In an objective lens of an optical pickup device for condensing light as a light spot via a transparent substrate of a medium, a first optical information recording medium having a transparent substrate having a thickness of t1 and a transparent substrate having a thickness of t2 using a light source having a wavelength of λ1. (However, t2
The light can be focused on the information recording surface of the second optical information recording medium of {t1), and the wavelength λ2 (where λ2 ≠)
At least one surface of the objective lens is constituted by a plurality of divided surfaces so that light can be focused on the information recording surface of the second optical information recording medium even when the light source of λ1) is used. An objective lens for an optical pickup device, comprising: 21. A semiconductor device having a plurality of divided surfaces at least one of which is divided concentrically with the optical axis and a second (n is an integer of 1 or more) optical axis side of a second (n) divided surface. The light transmitted through the 2n-1) divided surface and the light transmitted through the (2n + 1) -th divided surface opposite to the optical axis side from the 2n divided surface are substantially transmitted through the transparent substrate having a predetermined thickness. When the phase is the same, the light transmitted through the (2n-1) -th divided surface transmits through the second n-divided surface closer to the optical axis than the substantially central position of the second n-divided surface in a direction orthogonal to the optical axis. And the phase difference of (Δn
L) π (rad), and the phase difference between the light transmitted through the (2n + 1) -th divided surface and the light transmitted through the second n-th divided surface opposite to the optical axis side from the center position is (ΔnH) An objective lens for an optical pickup device, characterized by satisfying (ΔnH) ≠ (ΔnL) where π (rad). 22. A first optical information recording medium having a transparent substrate thickness t1 and a transparent substrate thickness t2 (where t2ｔt1).
The second optical information recording medium, the light flux emitted from the light source is condensed on the information recording surface via the transparent substrate by one condensing optical system, and the information is recorded on the information recording surface or the information recording surface is recorded. In the optical pickup device for reproducing the above information, at least one surface of the condensing optical system has a plurality of divided surfaces concentrically with the optical axis and a second n-th divided surface (where n Is an integer of 1 or more) and passes through the (2n-1) -th divided surface on the optical axis side and passes through the transparent substrate. The phase difference between light transmitted through the second n-th divided surface and passing through the transparent substrate is (ΔnL) π (rad), and the (2n + 1) -th divided surface on the side opposite to the optical axis side from the second n-th divided surface is Light transmitted through the transparent substrate and a second light beam on the opposite side of the optical axis side from the center position. An optical pickup device characterized by satisfying (ΔnH) ≠ (ΔnL), where (ΔnH) π (rad) represents a phase difference between light transmitted through the n-divided surface and passing through the transparent substrate. 23. A first optical information recording medium having a transparent substrate thickness t1 and a refractive index n1, and a transparent substrate thickness t2 (where t1
2 ≠ t1), focusing optics of an optical pickup device capable of recording or reproducing two types of optical information recording media, a second optical information recording medium having a refractive index n2 and a recording density smaller than the first optical information recording medium. In the system, a light beam from a recording or reproducing light source of the first optical information recording medium is condensed through a transparent substrate having a thickness of t1 and a refractive index of n1, and recording or reproducing of the first optical information recording medium is performed. When a beam spot is formed for the optical information recording medium,
From the numerical aperture NAL to the numerical aperture NAH (where NAH> NA
L) does not converge on the beam spot forming position, and the light beam from the recording or reproducing light source of the second optical information recording medium passes through a transparent substrate having a thickness t2 and a refractive index n2. When a beam spot for recording or reproduction of the second optical information recording medium is formed by condensing through the second optical information recording medium, when viewed from the optical information recording medium side,
Light beams from near the optical axis to NAH are condensed at the beam spot forming position, and light beams in a region having a higher NA than NAH are not condensed at the beam spot forming position.
A condensing optical system for an optical pickup device, wherein at least one surface of the condensing optical system is constituted by a plurality of divided surfaces concentric with an optical axis. 24. The transparent substrate having different thicknesses and different recording densities.
In a light-collecting optical system of an optical pickup device capable of recording or reproducing an optical information recording medium of a type, a light beam emitted from a light source is transmitted in a direction perpendicular to the optical axis in the order from the vicinity of the optical axis to a first light beam and a second light beam. At least one surface of the condensing optical system is constituted by a divided surface concentric with the optical axis so as to be divided into at least three light beams of a light beam and a third light beam. When reproducing, the first light flux and the second light flux near the optical axis of the light flux emitted from the light source are condensed on the information recording surface of the optical information recording medium, and recording or recording on the optical information recording medium having a large recording density is performed. A condensing optical system for an optical pickup device, wherein, during reproduction, the first light beam and the third light beam among the light beams emitted from a light source are condensed on an information recording surface of the optical information recording medium.