JP2002312974A - Optical head and optical disk device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain error-free an out-of-focus detection signal free of detection error from each of laser beams reflected on an optical disk using an optical head that has a plurality of semiconductor laser chips of different wavelengths. SOLUTION: For the purpose of making the focus position of each reflected beam coincident with the same surface of a semiconductor substrate having a photodetecting element, the semiconductor laser chips are arranged so that the position in the optical axis direction is deviated by a quantity determinable with the image-face curvature and chromatic aberration of the collimator lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording information on or reproducing information from an optical information medium such as an optical disk, and an optical disk apparatus using the same. The present invention relates to an optical head capable of recording and reproducing information using a laser module equipped with a plurality of semiconductor laser chips having different wavelengths, and an optical disk device using the same.

[0002]

2. Description of the Related Art An optical head used in an optical information recording / reproducing device such as an optical disk device is required to be reduced in size. Therefore, for example, in JP-A-6-274926, a plurality of photodetectors are formed on the surface of a semiconductor substrate, and a plane lower than the surface of the semiconductor substrate and a reflection surface are formed by etching, and the semiconductor laser chip is formed on the plane. A laser module installed thereon and an optical head using the laser module have been proposed. In this optical head, a laser beam emitted from a semiconductor laser chip is reflected by a reflection surface, bent in a direction perpendicular to the semiconductor substrate surface, emitted from a laser module, and irradiated on an optical disk by a lens. The reflected beam from the optical disc is diffracted by a diffraction grating provided on the surface of the cover plate of the laser module, the traveling direction of the beam is inclined, and is detected by a photodetector formed on the surface of the semiconductor substrate.

Generally, the image plane of light incident on a lens at various angles is not flat but curved. This property of the lens is called field curvature. In an ordinary convex lens, the focal position shifts toward the near side as the incident angle of the light beam is inclined from the main optical axis of the lens. The properties of this convex lens are described in
This is preferable for an optical head in which a semiconductor laser chip is installed at a position lower than the surface of a semiconductor substrate on which a photodetector is formed, as described in JP-274926A. That is,
Since the position of the light detecting element is shifted in the lens direction from the light emitting point of the semiconductor laser, it is possible to match the focal position of the obliquely incident light beam for detection with the position of the light detecting element,
An accurate defocus detection signal can be obtained. But,
In JP-A-6-274926, the thickness of the cover plate of the laser module is partially reduced in consideration of the case where it is difficult to make the focus position of the obliquely incident light beam for detection coincide with the position of the photodetector. A technique for changing the focal position of the reflected beam by changing the position is disclosed.

In recent years, CD-Rs (Compact Disk-Rs), which have become popular as writable optical disks, have been developed.
and a DVD (Digital V) developed as a higher density writable optical disc.
ersatile Disc / Digital Vid
eo Disc) There is a remarkable demand for recording and reproducing both optical disks of a DVD-RAM with the same small optical head. The laser wavelength suitable for recording / reproducing a CD-R is about 780 nm, while the laser wavelength suitable for recording / reproducing a DVD is about 660 nm.
It is necessary to mount both a laser light source of nm and a laser light source of a wavelength of about 660 nm on the same optical head. Therefore, for example, Japanese Patent Application Laid-Open No. 10-21577 discloses a CD semiconductor laser chip having a wavelength of about 780 nm and a wavelength of about 66 nm.
A small optical head has been proposed in which a 0 nm DVD semiconductor laser chip and a photodetector are integrated into one unit. This optical head is disclosed in Japanese Patent Laid-Open No. 6-274926.
As in the optical head of the publication, a plurality of photodetectors are formed on the surface of the semiconductor substrate, and the semiconductor substrate has a semiconductor laser chip mounting plane and a reflection surface lower than the surface. The two semiconductor laser chips having different wavelengths are arranged side by side on the installation plane.

[0005]

However, in the above-mentioned conventional example in which two semiconductor laser chips having different wavelengths and a photodetector are integrated, the two semiconductor laser chips are arranged along a direction perpendicular to the optical axis of the lens. Are located at different positions, the two beams are incident on the lens at different angles and are focused at different positions along the optical axis direction due to field curvature. Therefore, although it is possible to match the focal position of one of the beams with the position of the photodetector on the semiconductor substrate, the focal position of the other beam cannot be coincident with the position of the photodetector at the same time. Neither of the two laser beams can simultaneously obtain an error-free defocus detection signal. Further, in order to make the focal position of the other beam coincide with the position of the light detecting element, the above-mentioned Japanese Patent Application Laid-Open No.
Although it is conceivable to use a cover plate having a partially different thickness as disclosed in Japanese Patent No. 74926, however, not only is a new optical component required, but also two semiconductor laser chips and a light-receiving element come close to each other. Therefore, it is necessary to adjust the position of the cover plate. Therefore, there is a problem that the number of parts increases and the manufacturing cost also increases.

An object of the present invention is to provide an optical head for recording information on or reproducing information from an optical information medium by using a plurality of laser light sources, without using any new optical parts, and by using a plurality of laser beams. An object of the present invention is to provide a small-sized optical head and an optical disk apparatus using the same, which can obtain a defocus detection signal having no error.

[0007]

According to a first aspect of the present invention, there is provided a laser light source for emitting a plurality of laser beams having different wavelengths, a forward path from the laser light source to an information recording medium, and information. A lens disposed on the return path from the recording medium toward the laser light source, a beam separating means for separating the laser beam on the return path from the laser beam on the outward path at a different angle, and a plurality of detectors disposed near the laser light source and detecting the laser beam on the return path And a plurality of laser light sources are arranged at different positions along the outward direction while the plurality of light detection units are arranged on the same plane. In the second invention, the plurality of photodetectors are provided on the same substrate, and the substrate is provided with a reflection surface for reflecting the outward laser beam and a plane on which the plurality of laser light sources are arranged.

In the third invention, the reflecting surface is constituted by a plurality of reflecting surfaces.

In the fourth invention, the plane on which the plurality of laser light sources are arranged is constituted by a plurality of planes.

According to a fifth aspect of the present invention, a semiconductor laser chip for emitting a plurality of laser beams having different wavelengths, a lens for guiding the laser beam to an information recording medium, and a diffraction grating or hologram element for diffracting a reflected beam from the information recording medium And a plurality of photodetectors for detecting reflected beams from the information recording medium, wherein the plurality of photodetectors are formed on the same plane of the semiconductor substrate, and a reflection surface for reflecting the plurality of laser beams on the semiconductor substrate. And a plane on which a plurality of semiconductor laser chips are arranged, and the plurality of semiconductor laser chips are arranged at different positions along the laser beam emission direction.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical head according to the present invention and an optical disk apparatus using the same will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of an optical disk device according to the present invention, wherein FIG.
FIG. 1B is a side view of FIG.
FIG. 1C is a side view of FIG. 1A viewed from the direction of arrow C. 1A to 1C, the components denoted by the same numbers indicate the same components. In the figure, reference numeral 2 denotes an optical disk, specifically, a CD-R having a laser wavelength suitable for recording and reproduction of about 780 nm and a substrate thickness of 1.2 mm.
An OM disk or a CD-R disk, or a DVD disk having a laser wavelength suitable for recording or reproduction of about 660 nm and a substrate thickness of 0.6 mm. 3 is a motor,
The optical disk device 1 is fixed to the optical disk device 1 and rotates the optical disk 2 via the rotation shaft 4. 2 ′ indicates the rotation direction of the optical disk 2. Reference numeral 5 denotes an optical head which can be moved on the rail 7 in the radial direction of the optical disk 2 by an access mechanism 6 including a voice coil motor and a pulley. Optical head 5
Inside, a two laser module 8, a collimating lens 9, a mirror 10, and a lens actuator 11 are incorporated. 2 The laser module 8 has a wavelength of about 6
A semiconductor laser chip 13a that emits a 60 nm laser beam 12a and a semiconductor laser chip 13b that emits a laser beam 12b having a wavelength of about 780 nm are incorporated. The lens actuator 11 includes a composite element 14 combining a quarter-wave plate and a polarization diffraction grating.
And a focus lens 15 are attached. Next, the structure of the laser module according to the present invention will be described with reference to FIG. FIG. 2 is a configuration diagram showing one embodiment of a laser module according to the present invention, FIG.
FIG. 2B is a sectional view taken along line A1-A2 of FIG. In the figure, reference numeral 21 denotes a package formed of a material having good heat conductivity such as aluminum nitride, and has a plurality of lead wires 22 penetrated for transmitting electric signals. Package 2
A semiconductor substrate 24 made of silicon or the like is provided inside 1, and is sealed by a package 21 and a glass plate 23.
A concave portion 25 is formed in the semiconductor substrate 24 by etching or the like, and the slope of the concave portion 25 is a mirror surface 2 having an angle of about 45 degrees.
It is 6. The semiconductor laser chip 13a and the semiconductor laser chip 13b are mounted in the concave portion 25, and the laser beams 12a and 12b are emitted to the right in FIG. According to the present invention, the semiconductor laser chip 13b that emits a laser beam 12b having a wavelength of about 780 nm has a wavelength of about 660 nm.
2B from the semiconductor laser chip 13a that emits the m laser beam 12a, that is,
It is arranged rearward along the direction of travel of the laser beam. The laser beams 12a and 12b are reflected by the mirror surface 26, pass through the glass plate 23, and
Is emitted from. In FIG. 1C, laser beams 12a and 12b emitted from the two laser module 8 are shown.
Is converted into a parallel light beam by the collimating lens 9 and the mirror 10
Reflected by the composite element 14 of the lens actuator 11
And is incident on the focus lens 15. Next, FIG.
The lens actuator will be described with reference to FIG. 3A and 3B are configuration diagrams showing an example of a lens actuator used in the present embodiment. FIG. 3A is a top view of the lens actuator viewed from the direction of the optical disk, and FIG. 3 is a partial cross-sectional view in the B1-B2 direction of FIG. FIG.
In (b), the optical disc 2 is drawn for reference. In the figure, reference numeral 31 denotes a lens holder, on which a coil 34, a focus lens 15, and a composite element 14 are mounted under the coil 34, and which is held on a holding table 33 by a spring 32. The solid line 36 in FIG.
3 shows a surface of a housing of an optical head 5 for fixing 3 and the like. The lens actuator 11 controls the focus by driving the composite element 14 and the focus lens 15 in the vertical direction on the paper surface of FIG. 3B, and drives the composite device 14 and the focus lens 15 in the vertical direction on the paper surface (radial direction of the optical disk 2) of FIG. To perform tracking control. In this embodiment, the laser beams 12a and 12b emitted from the semiconductor laser chips 13a and 13b are combined with a composite element 14 composed of a polarizing four-division grating and a quarter-wave plate.
Is incident as an ordinary ray, for example. In this case, the laser beams 12a and 12b are transmitted without being diffracted at the polarizing diffraction grating portion, and
The light becomes circularly polarized light by the quarter-wave plate of 4. Optical disk 2
The laser beams 12a and 12b reflected by the laser beam 12a and 12b become extraordinary rays by passing through the quarter-wave plate of the composite device 14 again, and are diffracted by the polarizing four-division diffraction grating. Hereinafter, the 4-division diffraction grating will be described with reference to FIG.
FIG. 4 is a plan view showing an example of the diffraction grating pattern of the four-segment diffraction grating 40 constituting the composite device. As shown in the figure, the quadrant diffraction grating 40 is divided into four regions by boundary lines 41 and 42. A circle 43 indicates the laser beam 12a or the laser beam 12b, and the four-divided diffraction grating 40
By this, the light is separated into four + 1st-order diffracted lights and four -1st-order diffracted lights. In the diffraction gratings of the four regions, the directions of the grating grooves are different, but the intervals between the grating grooves are equal. Therefore, the eight ± first-order diffracted lights have different diffraction directions but the same absolute value of the diffraction angle. These eight diffracted lights are respectively condensed by the collimating lens 9, and are condensed by two semiconductor laser chips 13a. 13b
Are focused as eight spots on the surface of the semiconductor substrate 24 inside the laser module 8 having Hereinafter, a detailed example of the semiconductor substrate 24 inside the laser module 8 will be described with reference to FIG. FIG. 5 is a front view showing one embodiment of the semiconductor substrate inside the laser module shown in FIG. The semiconductor laser chip 13a and the semiconductor laser chip 13b are mounted in a concave portion 25 formed in a semiconductor substrate 24, and the laser beam 12b having a wavelength of about 780 nm
The semiconductor laser chip 13b that emits light has a wavelength of about 6
The semiconductor laser chip 13a that emits a 60-nm laser beam 12a is directed leftward in FIG.
It is arranged rearward along the direction of travel of the laser beam. The semiconductor laser chip 13a emits a laser beam 12a in the right direction on the paper, and the laser beam 12a is reflected at a position indicated by 51a on the mirror surface 26 and emitted in a direction perpendicular to the paper and on the front side of the paper. Similarly, the semiconductor laser chip 13b emits the laser beam 12b in the right direction on the paper surface, and the laser beam 12b is reflected at the position indicated by 51b on the mirror surface 26 and emitted in the direction perpendicular to the paper surface and on the front side of the paper surface. In the figure, eight black quarter circles indicate spots 52a of the laser beam 12a reflected by the optical disk 2 and separated by the four-divided diffraction grating 40,
It is on the circumference of a circle centered on position 51a. The eight white (unfilled) quarter circles are the laser beams 12 reflected by the optical disk 2 and separated by the four-divided diffraction grating 40.
b shows the spot 52b, which is on the circumference of a circle centered on the position 51b. 53-1a, 53-1b, 52-2a,
53-2b, 53-3a, 53-3b, 53-4a, 5
Reference numeral 3-4b denotes a light detecting element for obtaining a defocus detection signal. The light detecting elements 53-1a and 53-1b and the light detecting element 5 are a set of two opposing elongated light detecting elements.
3-2a and 53-2b, photodetectors 53-3a and 53-
3b, composed of four sets of photodetectors 53-4a and 53-4b, four spots 52a or four spots 52
b. The out-of-focus detection method uses a knife-edge method (Fouco method) using a four-divided beam, and each set of
Light receiving elements 53-1a and 53-1b, 52-2a and 5
3-2b, 53-3a and 53-3b, 53-4a and 53
By performing a difference operation on the output signal of −4b, a defocus detection signal can be obtained. However, in this embodiment, the light receiving elements are connected to each other by connecting the conductive thin films 54a and 54b of aluminum or the like as shown in the figure, and the output signals from the A terminal and the B terminal of the wire bonding pad 55 are subjected to a difference calculation.
Obtain a defocus detection signal. 56c, 56d, 56e, 5
Reference numeral 6f denotes four light detection elements for obtaining a track shift detection signal and an information reproduction signal, which are connected to the C terminal, the D terminal, the E terminal, and the F terminal of the pad 55. The signals output from the terminals A to F of the pad 55 are input to the block shown in FIG. 6, and necessary signals are obtained. FIG. 6 is a block diagram showing an embodiment of a signal operation circuit for obtaining a focus shift detection signal, a track shift detection signal, and an information reproduction signal. In the figure, reference numeral 61 denotes a differential circuit for subtracting output signals from the A terminal and the B terminal of the wire bonding pad 55 shown in FIG. 5, and outputs a defocus detection signal 62.
63-1 is an addition circuit for adding the output signals from the C terminal and the D terminal, and 63-2 is an addition circuit for adding the output signals from the E terminal and the F terminal. 63-3 is a differential circuit for subtracting the output signal of the addition circuit 63-1 and the output signal of the addition circuit 63-2, and a push-pull type track shift detection signal 64 when an optical disk having a guide groove or the like is used. Is output. Reference numeral 63-4 denotes an addition circuit for adding the output signal of the addition circuit 63-1 and the output signal of the addition circuit 63-2, and outputs an information reproduction signal 65. 66-1 is C
An adder circuit for adding the output signals from the terminal and the E terminal, and 66-2 is an adder circuit for adding the output signals from the D terminal and the F terminal. 66-3 is an addition circuit 66-1
A differential circuit for subtracting the output signal of the adder 66-2 and the output signal of the adder 66-2. The output signal 67 can be used to obtain a phase difference type track shift detection signal of an optical disk having guide pits and the like. These focus shift detection signals and track shift detection signals are supplied to the coil 34 of the lens actuator 11 shown in FIG.
By driving the focus lens 15 attached to the camera 1 in the optical axis direction and the disk radial direction, automatic focus control and track following control can be achieved. Therefore, information can be recorded on the optical disk 2 by modulating the light intensity of the laser beam 12a or the laser beam 12b emitted from the semiconductor laser chip 13a or 13b with the information recording signal.
Also, by keeping the light intensity of the laser beams 12a and 12b emitted from the semiconductor laser chips 13a and 13b constant,
The information recorded on the optical disc 2 can be reproduced from the information reproduction signal 65. Hereinafter, the principle of the optical head according to the present invention will be described with reference to FIG. FIG. 7A shows a part of an optical system of a conventional optical head. Reference numeral 13a denotes a semiconductor laser chip having a wavelength of about 660 nm, and reference numeral 71a denotes a light emitting point thereof. Reference numeral 13b denotes a semiconductor laser chip having a wavelength of about 780 nm, and reference numeral 71b denotes a light emitting point. Light emitting point 7
The light emitting point 1a and the light emitting point 71b are substantially aligned at a position about 210 μm apart in the horizontal direction of the drawing. Reference numeral 72 denotes a collimator lens, reference numeral 40 denotes a diffraction grating, and reference numeral 73 denotes a position on the semiconductor surface where the photodetector is formed. The laser beam 12a having a wavelength of 660 nm emitted from the light emitting point 71a is converted into a parallel light beam by the collimator lens 72, and is irradiated on the optical disk by a focus lens (not shown). The laser beam 12a 'having a wavelength of 660 nm reflected by the optical disk is
The light is diffracted by the diffraction grating 40 and obliquely enters the collimator lens 72. In general, light obliquely incident on a lens is different between a converging position in a cross section in the oblique incident direction (meridional section) and a converging position in a cross section in a direction perpendicular to the lens (spherical cross section). This is called spherical image field curvature. Since the amounts of the meridional field curvature and the spherical field curvature are different, astigmatism occurs in the focused beam obliquely incident.
Whether to use the converging position of the meridional field curvature of the laser beam having astigmatism or the converging position of the spherical missing field curvature for the defocus detection depends on the detection method and the shape of the photodetector. Here, the focus of the detection beam will be described using the approximate center of the meridional field curvature and the spherical missing field curvature, that is, the minimum circle of confusion. A curve 74a shows a focusing position when a laser beam having a wavelength of 660 nm is incident on the collimating lens 72 at various angles, that is, a field curvature. The collimating lens 72 has, for example, a focal length of about 9.3 mm and a structure in which two lenses are bonded together. The first lens on the laser side is made of LaF-2 glass material.
And the radius of curvature of the first surface on the laser side is about +6.7 mm,
The radius of curvature of the second surface bonded to the second lens is about -5.
The convex lens is 0 mm, and the distance between the first surface and the second surface is about 1.6 mm. Here, when the sign of the radius of curvature is positive, the spherical surface is convex on the laser side, and when the sign of the radius of curvature is negative, the spherical surface is convex on the diffraction grating side. The second lens on the diffraction grating side is made of SF-57 glass material, the radius of curvature of the first surface to be bonded to the second lens is approximately −5.0 mm, the radius of curvature of the second surface on the diffraction grating side is approximately −53 mm, The distance between the first surface and the second surface is a concave lens of about 0.9 mm. The grating pitch of the diffraction grating 40 is about 10.3 μm, and the laser beam 12 a ′ having a wavelength of 660 nm is about 3.
The light is incident on the collimating lens 72 inclined by 7 degrees,
Focus on The position of the convergence point 75a depends on the field curvature characteristic of the collimator lens 72 having the above-described configuration, and the luminous point 7a
1a is about 600 μm in the horizontal direction of the drawing and about 45 μm in the upward direction of the drawing. Therefore, if the position 73 of the semiconductor surface on which the light detecting element is formed is arranged at a position about 45 μm away from the light emitting point 71a in the upward direction in the drawing and the focusing point 75a and the position of the light detecting element are matched, the laser beam No detection error occurs in the defocus detection using 12a '.
Further, the collimator lens 72 having the above-described configuration is configured so that the chromatic aberration of the first convex lens is canceled by the chromatic aberration of the second concave lens, and the chromatic aberration is eliminated at the wavelengths of 660 nm and 780 nm. Therefore, the focus position when the laser beam having a wavelength of 780 nm is incident at various angles, that is, the curve 74b showing the field curvature is also a wavelength 660n.
It substantially matches the curve 74a for m. Therefore, if the semiconductor laser chip 13b having a wavelength of about 780 nm is arranged substantially at a position about 210 μm away from the semiconductor laser chip 13a in the horizontal direction in the drawing, the laser beam 12b emitted from the light emitting point 71b will be collimated by the collimating lens 72b.
It becomes almost parallel light beam. However, the laser beam 12b is inclined about 1.3 degrees with respect to the laser beam 12a. The laser beam 12b 'having a wavelength of 780 nm reflected by the optical disk is incident on the diffraction grating 40 at an inclination of about 1.3 degrees, is further inclined by about 4.3 degrees by diffraction, and is incident at an inclination of 5.6 on the collimating lens 72 to be focused. Focus on point 75b. The position of the focusing point 75b is determined by the light emitting point 71a due to the field curvature characteristic of the collimating lens 72 having the above-described configuration.
Approximately 900 μm in the horizontal direction of the drawing and approximately 9
0 μm apart. Therefore, the position of the focal point 75b is shifted from the position of the position 73 on the semiconductor surface on which the photodetector is formed by about 45 μm in the upward direction in the drawing, and the laser beam 12
In the defocus detection using b ', a detection error occurs. FIG. 7B shows a part of the optical system of the optical head according to the present invention. As in FIG. 7A, 13a has a wavelength of about 6
In the case of a semiconductor laser chip of 60 nm, 71a indicates its light emitting point, and 13b indicates a semiconductor laser chip of a wavelength of about 780 nm and 71b indicates its light emitting point. However, emission point 1
3a and the light emitting point 13b are approximately 210 μm in the horizontal direction of the drawing,
It is arranged at a distance of about 45 μm in the vertical direction of the drawing.
Numeral 40 indicates a diffraction grating, and numeral 73 indicates a position on the semiconductor surface on which the photodetector is formed. 76 is a collimating lens, and FIG.
As in the case of the collimating lens 72 shown in FIG. 7A, the focal length is about 9.3 mm and the two lenses are bonded together, and the radius of curvature and the distance between the lenses are almost the same. However, the glass material of the second lens on the diffraction grating side is LaSF-010, which has a lower dispersion than SF-57. Low dispersion glass material L for the second lens
By using aSF-010, the chromatic aberration of the concave lens becomes small, and the chromatic aberration of the first convex lens becomes remarkable as a whole of the collimating lens 76. Therefore, the wavelength 780
Curve 77b of field curvature for laser beam of nm
Is shifted downward by about 45 μm below the curve 77a for the wavelength of 660 nm. 660 nm wavelength laser beam 12a emitted from light emitting point 71a
7A, as in FIG. 7A, the light is focused at a focusing point 75a about 600 μm in the horizontal direction of the drawing and about 45 μm in the upward direction of the drawing. Therefore, if the position 73 of the semiconductor surface on which the light detecting element is formed is arranged at a position about 45 μm away from the light emitting point 71a in the upward direction in the drawing and the focusing point 75a and the position of the light detecting element are matched, the laser beam 12
No detection error occurs in defocus detection using a ′. On the other hand, since the semiconductor laser chip 13b having a wavelength of about 780 nm is arranged at a position about 45 μm downward in the drawing corresponding to the chromatic aberration of the collimating lens 76, the laser beam 12 emitted from the light emitting point 71b
b is a collimated lens and becomes a parallel light flux. The laser beam 12b 'having a wavelength of 780 nm reflected by the optical disk is
Again, the light enters the diffraction grating 40 at an inclination of about 1.3 degrees, and is further inclined by about 4.3 degrees by the diffraction action.
At an angle of 5.6, and converge at a focal point 75b. The position of the focusing point 75b is determined by the collimating lens 7 having the above-described configuration.
6, about 900 μm in the horizontal direction of the drawing and about 45 μm in the upward direction of the drawing due to the chromatic aberration and field curvature characteristics of No. 6.
m away. Therefore, the position of the focal point 75b coincides with the position of the position 73 on the semiconductor surface on which the photodetector is formed, and no detection error occurs even in defocus detection using the laser beam 12b '.

Referring to FIG. 7, the reflected beams 12a 'and 12a'
b ′ is a light detecting element 53-1a, 53-1b, 52-2a, 52-2b for obtaining the defocus detection signal of FIG.
The beams received at 53-3a, 53-3b, 53-4a, and 53-4b have been described. The beam separated in the direction opposite to the above beam by the diffraction effect of the diffraction grating 40 is:
Four photodetectors 56c, 56d, 56e and 56f for obtaining the track shift detection signal and the information reproduction signal of FIG.
The light is received. Although these beams are not focused on the photodetector surface, the four photodetectors 56c, 56d, 5d
There is no problem for 6e and 56f because only the light intensity of each beam needs to be detected. FIG. 8 is a front view showing another embodiment of the semiconductor substrate inside the laser module using the present invention. In the embodiment of the semiconductor substrate shown in FIG. 8, the light emitting point of the semiconductor laser chip 13a and the semiconductor laser chip 13b
5 are arranged so that the light emitting points are aligned in the vertical direction in the figure, and the reflecting surfaces are two reflecting surfaces 81a and 81a instead of the reflecting surface 26 in FIG.
1b, and the reflection surface 81b is set at a position shifted from the position of the reflection surface 81a by about 45 μm to the right in the drawing. By shifting the two reflecting surfaces in this way, FIG.
As described above, the same effect can be obtained as when the semiconductor laser chip is shifted in the optical axis direction. FIG. 9 is a front view showing still another embodiment of the semiconductor substrate inside the laser module using the present invention. In the embodiment of the semiconductor substrate shown in FIG. 9, the light emitting point of the semiconductor laser chip 13a and the light emitting point of the semiconductor laser chip 13b are arranged so as to be aligned in the vertical direction in the figure, and the reflecting surface is the same as the reflecting surface 26 of FIG. Are formed by the reflection surface 92. However, in this embodiment, two laser chip mounting surfaces 91a and 91b are used instead of the single concave portion 25 shown in FIG. 5, and the laser chip mounting surface 91b is about 45 μm deeper than the position of the laser chip mounting surface 91a. Etched. By shifting the depths of the installation surfaces 91a and 91b on which the two semiconductor laser chips are installed, the same effect as shifting the semiconductor laser chips in the optical axis direction as described with reference to FIG. 7 can be obtained.

[0013]

As described above, according to the present invention, when a laser light source having a plurality of wavelengths is used, both of a plurality of laser beams can obtain an error-free defocus detection signal.

[Brief description of the drawings]

FIG. 1 is a top view, a side view as viewed from a direction of an arrow B, and a side view as viewed from a direction of an arrow C, showing an embodiment of an optical disk device according to the present invention.

FIG. 2 is a front view showing a laser module according to an embodiment of the present invention, and a sectional view taken along line D1-D2.

FIG. 3 is a top view illustrating an example of a lens actuator used in the present embodiment, and is a partial cross-sectional view taken along a line E1-E2.

FIG. 4 is a plan view showing an example of a diffraction grating pattern of a four-segment diffraction grating constituting a composite device.

FIG. 5 is a front view showing one embodiment of a semiconductor substrate inside the laser module shown in FIG. 2;

FIG. 6 is a block diagram showing an embodiment of a signal calculation circuit for obtaining a focus shift detection signal, a track shift detection signal, and an information reproduction signal.

FIG. 7 is a partial view of an optical system for explaining an example of the principle of an optical head according to the present invention.

FIG. 8 is a front view showing another embodiment of the semiconductor substrate according to the present invention.

FIG. 9 is a front view showing another embodiment of the semiconductor substrate according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical disk, 6 ... Access mechanism, 7 ... Rail, 9 ...
Collimating lens, 10 mirror, 11 lens actuator, 13a semiconductor laser chip, 13b semiconductor laser chip, 15 focus lens, 81a
Mirror surface 81b Mirror surface 91a Semiconductor laser chip installation surface 91b Semiconductor laser chip installation surface

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasuyuki Arikawa 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Digital Media Products Division, Hitachi, Ltd. F-term (Reference) 5D118 AA01 AA13 AA26 BA01 BB03 BB07 CD02 DB07 5D119 AA01 AA28 AA41 BA01 BB02 BB04 EA03 EC03 EC45 EC47 FA08 JA57 KA04 LB02 LB04 LB06

Claims (6)

[Claims] 1. A laser light source for emitting a plurality of laser beams having different wavelengths, a lens disposed on a forward path from the laser light source to an information recording medium and a return path from the information recording medium to the laser light source; A beam separating means for separating the laser beam from the outgoing laser beam at a different angle, and a plurality of light detecting means arranged near the laser light source and detecting the backward laser beam, An optical head, wherein the means are arranged on the same plane, and the plurality of laser light sources are arranged at different positions along the outward path. 2. The optical head according to claim 1, wherein said plurality of light detecting means are provided on a same substrate, and said substrate is provided with a reflecting surface for reflecting said outward laser beam and said plurality of laser light sources. An optical head having a flat surface. 3. The optical head according to claim 2, wherein said reflection surface comprises a plurality of reflection surfaces. 4. The optical head according to claim 2, wherein the plane on which the plurality of laser light sources are arranged comprises a plurality of planes. 5. A semiconductor laser chip for emitting a plurality of laser beams having different wavelengths, a lens for guiding the laser beam to an information recording medium, a diffraction grating or a hologram element for diffracting a reflected beam from the information recording medium, A plurality of light detecting elements for detecting reflected beams from the information recording medium, the plurality of light detecting elements being formed on the same plane of a semiconductor substrate, and reflecting the plurality of laser beams to the semiconductor substrate. An optical head, comprising: a reflection surface and a plane on which the plurality of semiconductor laser chips are arranged; and the plurality of semiconductor laser chips arranged at different positions along a laser beam emission direction. 6. A laser beam from an optical head is applied to an optical information medium, and a laser beam reflected from the optical information medium is applied to a plurality of photodetectors. 6. An optical disk device for obtaining a control signal and an information reproduction signal from a signal converted into an optical head, comprising the optical head according to claim 1.