JP5000001B2 - Optical pickup lens - Google Patents

Description

  The present invention relates to an optical pickup lens used in an optical system that performs recording or reproduction on an optical disc.

In recent years, the recording capacity of optical discs continues to increase, and the recording density per unit area also continues to increase. In reading information from the optical disk, light from the light source of the optical disk device is used as a light path through a transparent component such as a wave plate or a collimator lens, and finally an optical pickup lens is used to form a light spot on the optical disk, Information on the optical disc can be read. Usually, light emitted from a laser light source is collimated by a collimator lens or the like and is incident on an optical pickup lens.
Here, in an optical pickup lens used for reading a large-capacity optical disk, laser light having a wavelength of 410 nm or less is used, and the numerical aperture NA is often 0.84 or more.

  Examples of conventional optical pickup lenses include those described in Patent Documents 1 to 3. The objective lens for an optical disk described in Patent Document 1 is a double-sided aspherical single lens having a numerical aperture of 0.7 or more, and the center thickness of the lens is longer than the focal length. The objective lens described in Patent Document 2 satisfies 1.1 ≦ d1 / f ≦ 3, where one surface is aspherical, d1 is the axial lens thickness, and f is the focal length. Further, the objective lens described in Patent Document 3 is an objective lens having a numerical aperture of 0.75 or more, and this objective lens is a single objective lens having both aspheric surfaces, and has a refractive index at at least one of the used wavelengths. If n is n and the Abbe number in the d-line is ν, 1.75 <n and 35 <ν are satisfied.

JP 2002-156579 A JP 2001-324673 A JP 2002-303787 A

  By the way, it is necessary to improve off-axis characteristics in order to attach the optical pickup lens to the pickup. However, when the numerical aperture NA is larger than 0.80, it becomes difficult to improve both the characteristics of axial aberration such as spherical aberration and off-axis aberration such as astigmatism and coma aberration of the pickup lens. In particular, a biconvex lens having a convex surface on the side close to the laser light source (R1 surface) and a surface on the opposite side (R2 surface) is difficult to have good field angle characteristics.

  Further, when the numerical aperture NA is larger than 0.80, the working distance (WD) indicating the distance between the optical pickup lens and the optical disk is decreased. A meniscus lens or the like whose R2 surface is not convex has a particularly small working distance, and the optical disk and the optical pickup lens may collide with each other.

  The present invention has been made to solve such problems, and in a high NA optical pickup lens, it is possible to ensure a longer working distance while having good on-axis characteristics and off-axis characteristics. An object of the present invention is to provide an optical pickup lens that can be used.

  An optical pickup lens according to the present invention is an optical pickup lens that condenses a light beam from a laser light source onto an optical information recording medium, and the lens is a single lens, and is close to the laser light source among the two surfaces. The surface shape of the second surface opposite to the first surface is a continuous shape, with a radius h1, a radius h2, and a radius h3 (h1 <h2 <h3) from the optical axis toward the lens outer diameter. In this case, when the sag amounts at the radius h1, the radius h2, and the radius h3 are sag1, sag2, and sag3, and the amount of change of each sag is Δsag1, Δsag2, and Δsag3, 0> Δsag1> Δsag2 and Δsag2 <Δsag3 There are satisfying h1, h2, and h3.

  In the present invention, since the surface shape of the second surface satisfies 0> Δsag1> Δsag2 and Δsag2 <Δsag3, a working distance (distance between the optical pickup lens and the optical disk) can be sufficiently secured, A lens having good axial aberration characteristics can be obtained.

  The surface shape of the second surface includes h1, h2, h3, and h4 that satisfy sag2> sag3 and sag3 <sag4 when the sag amount at the lens radius h4 (h3 <h4) is sag4. It is preferable. Alternatively, the surface shape of the second surface may be h1, h2, h3 satisfying Δsag3 <0 and Δsag4> 0 when the sag amount at the lens radius h4 (h3 <h4) is sag4 and the sag change amount is Δsag4. , H4 are preferably present. Alternatively, the shape of the second surface preferably has a minimum value. Alternatively, it is preferable that the second surface has a surface shape having a convex central portion and a concave outer peripheral portion. By satisfying these conditions, a sufficient working distance can be secured, and better on-axis characteristics and off-axis characteristics can be obtained.

  Furthermore, it is used in a recording and / or reproducing pickup device using a laser having a wavelength of 410 nm or less, and when NA is the numerical aperture, d is the center thickness of the single lens, and f is the focal length of the objective lens, 0.84 ≦ It is preferable to satisfy NA and 0.9 ≦ d / f.

  In this case, it is used in a recording and / or reproducing pickup device using a laser with a wavelength of 410 nm or less, and when the numerical aperture is NA, the single lens center thickness is d, and the focal length of the objective lens is f, 0.84 More preferably, ≦ NA and 0.9 ≦ d / f ≦ 1.2 are satisfied. By satisfying this condition, an appropriate edge thickness can be ensured, and the surface shape of the second surface that satisfies 0> Δsag1> Δsag2 and Δsag2 <Δsag3 can be easily manufactured.

  Furthermore, the refractive index n at a wavelength of 405 nm is preferably 1.51 ≦ n ≦ 1.64.

  In this case, the refractive index n at a wavelength of 405 nm is more preferably 1.59 ≦ n ≦ 1.62. By satisfying these conditions, an appropriate edge thickness can be secured, and the second surface satisfying 0> Δsag1> Δsag2 and Δsag2 <Δsag3 can be easily designed.

  The effective diameter D of the single lens is preferably 1.8 ≦ D ≦ 3.2 mm. By applying the present invention to a lens having this effective diameter, the effects of ensuring the working distance length and improving the on-axis characteristics and off-axis characteristics are exhibited.

  Furthermore, as an off-axis characteristic, it is preferable that the aberration is 15 mλrms or less when the angle of view is 0.3 degrees.

  Furthermore, it is preferable that the tangent angle α of the first surface is 60 ° ≦ α. As the tangent angle α increases, the sag amount of the first surface increases, and accordingly, the sag amount of the second surface decreases. Therefore, the second surface shape satisfying 0> Δsag1> Δsag2 and Δsag2 <Δsag3 is obtained. Easy to manufacture.

  The Abbe number νd of the lens material is preferably 50 ≦ νd. Thereby, a pit row can be accurately written on the optical disc. The larger the Abbe number, the stronger the lens against the wavelength jump at the time of writing.

  Furthermore, parallel light or weak finite light may be incident from the first surface side. The single lens may be a plastic material or a glass material.

  According to the present invention, it is possible to provide an optical pickup lens capable of ensuring a longer working distance while having good on-axis characteristics and off-axis characteristics in an optical pickup lens having a high NA.

(A) is a figure which shows the optical pick-up lens concerning embodiment of this invention, (b) is a schematic diagram which expands and shows the part enclosed with the broken line in (a). (A) is a figure which shows the other optical pick-up lens concerning embodiment of this invention, (b) is a schematic diagram which expands and shows the part shown with the broken line of (a). It is a figure explaining lens center thickness d of the optical pick-up lens concerning an embodiment of the invention, effective diameter D, and working distance WD. It is a figure which shows the wavefront aberration in the Example concerning this invention. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 1 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 1. FIG. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 2 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 2. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 3 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 3. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 4 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 4. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 5 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 5. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 6 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 6. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 7 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 7. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 8 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 8. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 9 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 9. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 10 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 10. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 11 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 11. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 12 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 12. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 13 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 13. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 14 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 14. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 15 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 15. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 16 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 16. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 17 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 17. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 18 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 18. FIG. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 19 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 19. FIG. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 20 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 20. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 21 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 21. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 22 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 22. FIG. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 23 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 23. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 24 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 24. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 25 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 25. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 26 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 26. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 27 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 27. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 28 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 28. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 29 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 29. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 30 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 30. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 31 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 31. It is a figure which shows the characteristic value of the optical pick-up lens concerning Example 32 of this invention. (A) is longitudinal aberration, (b) is a sag amount in the radial direction, and (c) is a diagram showing an optical pickup lens according to Example 32.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to an optical pickup lens for recording / reproducing information on / from an optical information recording medium.

  FIG. 1A is a diagram showing an optical pickup lens according to an embodiment of the present invention. FIG. 1B is a diagram for explaining the sag amount of the optical pickup lens, and is a schematic diagram showing an enlarged portion surrounded by a broken line in FIG. As shown in FIG. 1, of the two surfaces of the optical pickup lens 1a according to the present embodiment, which is a single lens, the opposite side to the first surface (hereinafter referred to as R1 surface) 11 close to the laser light source, that is, The second surface (hereinafter referred to as R2 surface) 12a, which is the surface facing the optical disk 30 composed of the optical disk substrate 32 and the optical transmission layer 31 in the optical disk, has the following surface shape.

That is, when the radius h1 <radius h2 <radius h3 toward the lens outer diameter and the sag change amounts of the radius h1, the radius h2, and the radius h3 are Δsag1, Δsag2, and Δsag3, the surface shape of the R2 surface 12 is the following ( The relationship of 1) and (2) is satisfied.
0>Δsag1> Δsag2 (1)
Δsag2 <Δsag3 (2)

First, the sag sag and the sag change amount Δsag will be described. FIG. 1B schematically shows from the center h0 of the R2 surface 12b to the outer peripheral end 13b. As shown in FIG. 1B, the sag amount (sag) is the lens center h0 at an arbitrary radius h when the optical axis of the optical pickup lens 1 and the lens center h0 of the R2 surface are aligned. The distance from the perpendicular L of the optical axis to the R2 plane. The direction from the R1 surface 11 to the R2 surface 12a is positive.
The sag change amount Δsag is the sag inclination amount at an arbitrary radius h in the R2 surface 12a, that is, the inclination from the straight line L of the tangent line of the R2 surface at the radius h. A case where the sag amount increases from the inner periphery toward the outer periphery is positive, and a case where the sag amount decreases is negative.

In FIG. 1, when the sag amounts corresponding to the radii h1, h2, and h3 are respectively sag1, sag2, and sag3,
h1 <h2 <h3sag1>sag2> sag3
It has become.

  FIG. 2A is a diagram showing another optical pickup lens according to the embodiment of the present invention, and FIG. 2B is a schematic diagram showing an enlarged portion indicated by a broken line in FIG. is there. The shape shown in FIG. 2 may be sufficient as well as the shape shown in FIG. That is, as shown in FIG. 2, the R2 surface 12b has a surface shape that satisfies the above formulas (1) and (2) and has a minimum value k (radius hk).

Here, having a minimum value means that the radius h1 <h2 <h3 <h4 and the sag amounts are sag1, sag2, sag3, sag4, respectively.
sag1>sag2> sag3 (3)
sag3 <sag4 (4)
It indicates that the relationship is satisfied. That is, the R2 surface 12b has radii h1 to h4 that satisfy the expressions (3) and (4).

Further, in this case, when the lens radii h1, h2, h3, and h4 satisfy h1 <h2 <h3 <h4, and the sag change amounts at the radii h1, h2, h3, and h4 are Δsag1, Δsag2, Δsag3, and Δsag4. , H1 to h4 satisfying Expression (5) as well as Expressions (1) and (2).
0>Δsag1> Δsag2 (1)
Δsag2 <Δsag3 <0 (2)
Δsag4> 0 (5)

  In FIG. 1, the central portion has a surface shape of a convex lens such that the inclination (Δsag) from the lens center h0 toward the outside gradually decreases and then decreases gradually. In FIG. 2, there is a concave portion on the peripheral edge portion, and the surface shape is such that the concave and convex portions are repeated when viewed in the radial direction. That is, the R2 surface 12b of the optical pickup lens shown in FIG. 2 has a surface shape in which the central portion is convex and the outer peripheral portion is concave.

  The R2 surface of the optical pickup lens shown in FIGS. 1 and 2 has a continuous shape, and does not have a stepped annular zone structure like a diffractive lens. However, it is not prohibited to provide a few steps to the extent that the technical idea of the present invention is not impaired. The R1 surface may be either a continuous shape or a ring zone structure with a step.

  Further, it is sufficient that the R2 surface of the optical pickup lens has a continuous inclination. When the R2 surface shape is continuous and when the R2 surface shape is continuous, a part of the lens surface is divided into an optical axis. Includes shapes that are translated in the direction.

  Having such a surface shape of the R2 surface 12a or 12b has the following effects. That is, a normal pickup lens is a biconvex lens having convex surfaces on both sides, or a meniscus lens composed of a convex lens and a concave lens. Each lens has its characteristics. When the distance between the center of the R2 surface and the distance to the disk 30 is a working distance (WD), the meniscus lens has a concave R2 surface, so that the working distance is larger than that of the biconvex lens. Will be shorter. On the other hand, the off-axis field angle characteristic shows that the meniscus lens is better than the convex lens because both surfaces are curved in the same direction.

  On the other hand, in the optical pickup lens 1a or 1b according to the present embodiment, since the concave portion is formed on the outer peripheral side and the convex portion is formed in the central portion, both the meniscus lens and the biconvex lens are provided. The characteristics can be satisfied. In other words, the working distance is long, and the angle-of-view characteristic can be improved as the off-axis characteristic while satisfying the on-axis characteristic.

  That is, in the optical pickup lens 1a shown in FIG. 1, the sag amount gradually increases from the radial center h0 of the R2 surface 12a toward the outer periphery 13a, and the sag amount after a radius h3 in FIG. It does not change. In the optical pickup lens 1b shown in FIG. 2, the amount of sag gradually increases from the radial center h0 of the R2 surface 12b toward the outer periphery 13b, and when reaching a certain radius, in this example, the radius h4, Up to 13b, the sag amount gradually decreases in contrast to the previous case. From the position where the increase / decrease amount of the sag amount changes, the inner diameter has a characteristic of a biconvex lens, and the outer diameter can have the characteristics of a meniscus lens.

In other words, since the center part of the lens is a biconvex lens, the working distance can be lengthened, and since it does not have a very large radius of curvature, it is possible to improve the angle of view characteristics while being a biconvex lens. is there. Then, by providing the meniscus feature on the outer diameter side (outer peripheral portion of the R2 surface) from the position where the increase / decrease amount of the sag amount is changed, it is possible to obtain a favorable field angle characteristic which is a feature of the meniscus lens. Further, since the portion corresponding to the meniscus lens is formed in the outer peripheral portion instead of the lens central portion, the working distance is not shortened. As described above, the optical pickup lenses 1a and 1b according to the present embodiment incorporate the features of the meniscus lens by forming the outer peripheral portion to be substantially flat or concave, and the inner peripheral portion to form the convex portion to form the biconvex lens. By incorporating the features, a long working distance can be secured, and the angle of view characteristics as well as the on-axis characteristics can be improved.
From the above viewpoint, it is preferable that the radii h1 to h4 in FIGS. 1 and 2 are all present in the region through which the laser beam passes.

  In the optical pickup lens 1a shown in FIG. 1, the meniscus shape is formed from the position of the radius h3 where the increase / decrease amount of the sag changes to the outer diameter, but the optical pickup lens 1b shown in FIG. 2 has a minimum value k. The meniscus shape is extremely extreme. By adopting such a shape, the working distance can be further increased, and the angle of view characteristics can be further improved as on-axis characteristics and off-axis characteristics.

Here, when the optical pickup lenses 1a and 1b are used in a recording and / or reproducing pickup device using a wavelength of 410 nm or less as a laser used in an optical head and an optical disk device, the following expression is satisfied. Is preferred.
0.84 ≦ NA
0.9 ≦ d / f ≦ 1.2

  NA represents the numerical aperture of the optical pickup lens. Further, d is a single lens center thickness of the optical pickup lens (see FIG. 3), and f is a focal length.

  Here, if the numerical aperture NA is smaller than 0.84, the effective diameter of the R2 surface is also reduced accordingly. When the effective diameter of the R2 surface is reduced, as described above, it is difficult to form the coupling portion between the biconvex lens and the meniscus lens in the outer peripheral portion of the R2 surface. Therefore, the numerical aperture NA is preferably 0.8 or more, and more preferably 0.84 or more.

  In general, from the viewpoint of working distance, it is preferable to reduce the center thickness d and the refractive index n. However, in order to make the numerical aperture NA larger than 0.84, increase the working distance, and improve the angle of view characteristics, the lens performance, that is, the relationship d / f between the focal length f and the center thickness d is specified. It is preferable to do.

  First, the reason why it is preferable to set d / f to 0.9 or more will be described. When the focal length f is a fixed value, the value of d / f decreases as the center thickness d decreases. When the value of d / f is decreased, the distance (edge thickness) at the end of each surface diameter of the R1 surface and the R2 surface is decreased. If the edge becomes thin, problems such as breaking of the edge occur, and it becomes difficult to attach the lens. Further, since f = h / NA (f: focal length, h: radius), there is a relationship of d / f = d × NA / h. As described above, the numerical aperture NA is 0.84 or more. Therefore, when NA is a fixed value, the larger the radius is, the smaller the value of d / f becomes. If the center thickness d is not increased accordingly, a sufficient edge thickness cannot be secured. . Therefore, d / f is preferably 0.9 or more.

  Further, by setting d / f to 1.2 or less, the surface shape of the R2 surface can be easily formed. Therefore, d / f is preferably 1.2 or less.

  Thus, by setting the numerical aperture NA to 0.84 or more and d / f to at least 0.9 or more, it becomes easy to design the optical pickup lens having the shape shown in FIGS. 1 and 2, and the working distance is increased. The angle of view can be improved as well as the on-axis characteristics.

  The refractive index is preferably set to 1.51 ≦ n ≦ 1.64. Here, n represents the refractive index of a blue-violet laser having a wavelength of 405 nm. When the refractive index n is smaller than 1.51, the curvature is larger than that of a lens having the same center thickness and a large refractive index, and the edge thickness that is the distance between the surface diameter ends of the R1 surface and the R2 surface is small. Therefore, the refractive index is preferably 1.51 or more.

  On the other hand, when the refractive index n is larger than 1.64, it is difficult to maintain the shape of the R2 surface of the present invention having both the shape of the biconvex lens and the meniscus lens, and it becomes easy to form a complete meniscus lens. Therefore, the refractive index n is preferably 1.64 or less. However, when the central portion of the R2 surface is convex and a concave portion can be formed on the outer peripheral portion, the refractive index n may be larger than 1.64. Of course.

  The refractive index is more preferably set to 1.59 ≦ n ≦ 1.62. By setting the refractive index n to 1.59 to 1.62, it becomes easy to design the optical pickup lens having the shape shown in FIG. Therefore, the refractive index is more preferably 1.59 to 1.62.

  By setting the refractive index n to 1.51 to 1.64, more preferably 1.59 to 1.62, it becomes possible to design an optical pickup lens having the shape shown in FIGS. 1 and 2, and a long working distance. Can be ensured, and on-axis characteristics and angle-of-view characteristics can be improved. The optical pickup lens has a practical lens diameter.

  Furthermore, the effective diameter D (see FIG. 3) is preferably 1.8 ≦ D ≦ 3.2 mm. If the effective diameter D is larger than 3.2 mm, the working distance becomes too wide and it is difficult to manufacture. On the other hand, if the effective diameter D is smaller than 1.8 mm, the working distance becomes too small to be practical. Therefore, the effective diameter D is preferably 1.8 to 3.2 mm.

  Furthermore, it is preferable that the tangential angle α of the R1 surface, which is a surface close to the laser light source, of the two surfaces of the single lens of the optical pickup lens is 60 ° ≦ α. When the tangent angle α is increased, the sag amount on the R1 surface is increased, and accordingly, the sag amount on the R2 surface is decreased. Accordingly, the shape of the optical pickup lens shown in FIG. On the other hand, when the tangent angle α is smaller than 60 degrees, the sag amount on the R1 surface is decreased, and the sag amount on the R2 surface is increased. If it does so, it will become difficult to manufacture the shape of R2 surface, and an angle-of-view characteristic will worsen. Therefore, the tangent angle α of the R1 surface is preferably 60 ° or more. As a result, the shape of the R2 surface can be easily manufactured, and on-axis characteristics and good field angle characteristics can be obtained.

Further, the Abbe number νd is preferably 50 ≦ νd. The larger the Abbe number, the better the characteristic chromatic aberration of the pickup lens. Chromatic aberration refers to the shift of the best spot position when the wavelength is shifted by +1 nm. In the pickup lens, the laser power is increased when recording, but a phenomenon occurs in which the wavelength temporarily shifts to the long wavelength side in order to increase the laser power. If the best spot position is shifted during recording, tracking is lost and recording at the best spot position becomes difficult. Therefore, in order to maintain good recording characteristics, it is necessary to increase the Abbe number νd. Here, the Abbe number νd is inversely proportional to the refractive index. As described above, the refractive index is preferably 1.51 ≦ n ≦ 1.64. However, in the case of the refractive index in this range, the Abbe number is about 50 ≦ νd ≦ 81.
Thus, the Abbe number is preferably 50 or more, and more preferably 60 or more.

  Next, an embodiment to which the present invention is applied will be described. FIG. 4 shows the wavefront aberration in each of Examples 1 to 32. Further, Example 1 corresponds to FIGS. 5 and 6, Example 2 corresponds to FIGS. 7 and 8, and Example 3 corresponds to FIGS. 9 and 10, respectively. Up to 68 Example 32 are supported. Here, Examples 1 to 4 are examples corresponding to the optical pickup lens 1a shown in FIG. Further, Examples 5 to 32 are examples corresponding to the optical pickup lens 1b shown in FIG. For example, in Example 1, FIG. 5 shows characteristic values of the optical pickup lens. 6A shows longitudinal aberration, FIG. 6B shows the sag amount from the center position of the R2 surface to the outer diameter, and FIG. 6C shows the optical pickup lens of the first embodiment. Yes.

  Next, each coefficient in Examples 1 to 34 will be described. First, equation Z1 (h1) of the curve of the optical pickup lens R1 surface is expressed as equation (6).

ここで、
Ｚ１（ｈ１）：光軸からｈ１の高さにおける光ピックアップレンズＲ１面のサグｈ１：光軸からの高さｋ１：光ピックアップレンズＲ１面の円錐係数Ａ１４、Ａ１６、Ａ１８、Ａ１１０、Ａ１１２、Ａ１１４、Ａ１１６：光ピックアップレンズＲ１面の非球面係数Ｒ１：Ｒ１面の曲率半径を示す。

here,
Z1 (h1): Sag of the optical pickup lens R1 surface at a height h1 from the optical axis h1: Height from the optical axis k1: Conical coefficients A14, A16, A18, A110, A112, A114 of the optical pickup lens R1 surface A116: Aspherical coefficient R1 of the optical pickup lens R1 surface R1: A radius of curvature of the R1 surface.

  Next, the equation Z2 (h2) of the curve of the optical pickup lens R2 surface is expressed as (7) below.

ここで、
Ｚ２（ｈ２）：光軸からｈ２の高さにおける光ピックアップレンズＲ２面のサグ
ｈ２：光軸からの高さ
ｋ２：光ピックアップレンズＲ２面の円錐係数
Ａ２４、Ａ２６、Ａ２８、Ａ２１０、Ａ２１２、Ａ２１４、Ａ２１６：光ピックアップレ
ンズＲ２面の非球面係数
Ｒ２：Ｒ２面の曲率半径
を示す。

here,
Z2 (h2): Sag of the optical pickup lens R2 surface at a height of h2 from the optical axis h2: Height from the optical axis k2: Conic coefficients of the optical pickup lens R2 surface A24, A26, A28, A210, A212, A214, A216: Aspherical coefficient of the optical pickup lens R2 surface R2: Indicates the radius of curvature of the R2 surface.

Next, a first embodiment shown in FIGS. 5 and 6 representing the optical pickup lens 1a shown in FIG. 1, and a fifth embodiment shown in FIGS. 13 and 14 representing the optical pickup lens 1b shown in FIG. 2 will be described. . Example 1 is a single lens (optical pickup lens) and optical disc according to Example 1 having the radius of curvature R, the surface interval d, the refractive index n of refraction at a wavelength of 405 nm, and the Abbe number νd shown in FIG. In contrast, longitudinal aberration was measured. FIG. 6A shows the result. FIG. 5B shows the focal length d, working distance WD, numerical aperture NA, and effective diameter of the optical pickup lens according to Example 1. FIG. 5C shows the aspheric coefficients of the R1 and R2 surfaces. FIG. 5 (d) shows a schematic diagram of the optical pickup lens in FIG. 6 (c). FIG. 6B shows the shape of the R2 surface with the horizontal axis from the center h0 to the outer diameter end (effective diameter), and the vertical axis taking the sag amount. In the first embodiment, as shown in FIG. 6B, 0>Δsag1> Δsag2 (1) in the range of the effective lens diameter as in the optical pickup lens 1a shown in FIG.
Δsag2 <Δsag3 (2)
And h1 <h2 <h3
sag1>sag2> sag3
It can be seen that As shown in FIG. 6A, the optical pickup lens according to Example 1 having such an R2 surface was able to obtain good longitudinal aberration up to the lens effective diameter. In addition, as shown in FIG. 4, good field angle characteristics could be obtained.

Further, in Example 2, as shown in FIG. 14B, similarly to the optical pickup lens 1b shown in FIG.
sag1>sag2> sag3 (3)
sag3 <sag4 (4)
And 0>Δsag1> Δsag2 (1)
Δsag2 <Δsag3 <0 (2)
Δsag4> 0 (5)
It can be seen that As shown in FIG. 14A, the optical pickup lens according to Example 11 having such an R2 surface was able to obtain good longitudinal aberration up to the lens effective diameter. In addition, as shown in FIG. 4, good field angle characteristics could be obtained.

  Similarly, in the other examples, good longitudinal aberration was obtained up to the lens effective diameter, and good field angle characteristics were obtained as shown in FIG.

  That is, as shown in FIG. 4 and FIGS. 5 to 68, in Examples 1 to 32, the optical pickup lens having a high NA has a long working distance while having good sine conditions and off-axis characteristics. A pickup lens could be produced.

DESCRIPTION OF SYMBOLS 1a, 1b Optical pick-up lens 11 R1 surface 12a, 12b R2 surface 21 Aperture 30 Optical disk 31 Optical-transmission layer 32 in optical disk Optical disk substrate

Claims (2)

A first surface on which a light beam from a laser light source is incident, and a second surface on the side opposite to the optical disk formed of an optical disk substrate on the side opposite to the first surface and a light transmission layer in the optical disk, and has a wavelength exclusively. Effective with a numerical aperture NA of 0.84 ≦ NA ≦ 0.87 for converging a luminous flux of visible light from the laser light source of 410 nm or less onto the optical disc at both an angle of view of 0 ° and an angle of view of 0.3 ° A single lens having a diameter D of 2.0 ≦ D ≦ 2.1 mm and a curvature radius r1 of the first surface of 0.751238 mm ≦ r1 ;
When the radius h1, radius h2, and radius h3 (h1 <h2 <h3) are set from the optical axis toward the lens outer diameter, the second surface has sag amounts at the radius h1, radius h2, and radius h3. When sag1, sag2, and sag3 are set, and the amount of change of each sag is Δsag1, Δsag2, and Δsag3, the surface shape has h1, h2, and h3 that satisfy Δsag1> Δsag2 and Δsag2 <Δsag3, and has a wavelength of 405 nm. refractive index n 1.51 ≦ n ≦ 1.57 der of is, the relative parallel light or weak finite light from the laser light source, the light surface distance 0 from the surface of the optical disk light transmission layer in the disk. an optical pickup lens according to claim condenser to Rukoto at the position of 0875Mm. 2. The optical pickup lens according to claim 1, wherein a radius of curvature r <b> 2 of the first surface satisfies −1.78333 mm ≦ r <b> 2.

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