JP4240769B2 - Optical pickup lens - Google Patents

Description

【００３８】
〔屈折率及び屈折率分布係数（ｄ線）〕
N0=1.80518
N2=-8.51778×10^-3
N4= 5.34182×10^-2
N6=-5.91190×10^-3
【００３９】
〔屈折率及び屈折率分布係数（Ｃ線）〕
N0=1.79610
N2=-8.48217×10^-3
N4= 5.32367×10^-2
N6=-5.82036×10^-3
【００４０】
〔屈折率及び屈折率分布係数（Ｆ線）〕
N0=1.82776
N2=-8.60387×10^-3
N4= 5.38535×10^-2
N6=-6.12383×10^-3
【００４１】
〔第１面(s1)の非球面データ〕
ε=1
A4= -1.12666×10^-2
A6= -2.54647×10^-2
A8= -5.25437×10^-3
A10=-3.27467×10^-3
【００４２】
〔第２面(s2)の非球面データ〕
ε=1
A4= -1.96267×10^-2
A6= -2.74829×10^-3
A8= -4.96284×10^-4
A10=-4.35596×10^-5
【００４３】
〔第３面(s3)の非球面データ〕
ε=1
A4= 1.12666×10^-2
A6= 2.54647×10^-2
A8= 5.25437×10^-3
A10= 3.27467×10^-3
【００４４】
〔第４面(s4)の非球面データ〕
ε=1
A4= -1.96267×10^-2
A6= -2.74829×10^-3
A8= -4.96284×10^-4
A10=-4.35596×10^-5
【００４５】

【００４６】
〔屈折率及び屈折率分布係数（ｄ線）〕
N0=1.80518
N2=-2.15427×10^-2
N4= 1.93470×10^-2
【００４７】
〔屈折率及び屈折率分布係数（Ｃ線）〕
N0=1.79610
N2=-2.14399×10^-2
N4= 1.92542×10^-2
【００４８】
〔屈折率及び屈折率分布係数（Ｆ線）〕
N0=1.82776
N2=-2.18173×10^-2
N4= 1.95936×10^-2
【００４９】
〔第２面(s2)の非球面データ〕
ε=1
A4= -4.56298×10^-3
A6= 1.22155×10^-5
A8= 2.30733×10^-4
A10=-7.40261×10^-5
【００５０】
〔第４面(s4)の非球面データ〕
ε=1
A4= -4.56298×10^-3
A6= 1.22155×10^-5
A8= 2.30733×10^-4
A10=-7.40261×10^-5
【００５１】

【００５２】
〔屈折率及び屈折率分布係数（ｄ線）〕
N0=1.80518
N2=-1.88189×10^-2
N4= 3.78850×10^-2
【００５３】
〔屈折率及び屈折率分布係数（Ｃ線）〕
N0=1.79610
N2=-1.87283×10^-2
N4= 3.76971×10^-2
【００５４】
〔屈折率及び屈折率分布係数（Ｆ線）〕
N0=1.82776
N2=-1.90597×10^-2
N4= 3.83653×10^-2
【００５５】
〔第２面(s2)の非球面データ〕
ε=1
A4= -1.11176×10^-2
A6= 3.42294×10^-4
A8= 3.15786×10^-4
A10=-9.32458×10^-5
【００５６】
〔第４面(s4)の非球面データ〕
ε=1
A4= -1.11176×10^-2
A6= 3.42294×10^-4
A8= 3.15786×10^-4
A10=-9.32458×10^-5
【００５７】

【００５８】
〔屈折率及び屈折率分布係数（ｄ線）〕
N0=1.80518
N2=-1.60621×10^-2
N4= 1.88522×10^-2
N6=-2.52711×10^-13
N8=-1.30901×10^-18
【００５９】
〔屈折率及び屈折率分布係数（Ｃ線）〕
N0=1.79610
N2=-1.63944×10^-2
N4= 1.87068×10^-2
N6=-4.48542×10^-13
N8=-2.60300×10^-18
【００６０】
〔屈折率及び屈折率分布係数（Ｆ線）〕
N0=1.82776
N2=-1.52353×10^-2
N4= 1.92167×10^-2
N6=-3.25885×10^-12
N8= 4.19719×10^-18
【００６１】
〔第１面(s1)の非球面データ〕
ε=1
A4= 1.19299×10^-2
A6= -1.74204×10^-3
A8= -9.99859×10^-4
A10= 3.79001×10^-4
【００６２】
〔第３面(s3)の非球面データ〕
ε=1
A4= -1.19299×10^-2
A6= 1.74204×10^-3
A8= 9.99859×10^-4
A10=-3.79001×10^-4
【００６３】
図５〜図８は、実施例１〜実施例４にそれぞれ対応する収差図であり、各々左から順に、球面収差，非点収差，歪曲収差を示している。球面収差図において、縦軸は記録面への入射高さをその最大高さで規格化した値であり、横軸は焦点位置（近軸結像位置からの光軸方向のズレ量）(mm)である。そして、実線によるラインＣはＣ線（波長656.3nm）に対する球面収差量、点線によるラインｄはｄ線（波長587.6nm）に対する球面収差量、一点鎖線によるラインＦはＦ線（波長486.1nm）に対する球面収差量をそれぞれ表している。
【００６４】
非点収差図において、縦軸は半画角(deg)であり、横軸は焦点位置（近軸結像位置からの光軸方向のズレ量）(mm)である。そして、点線Ｓはサジタル面での非点収差量を表している。また、二点鎖線Ｔはタンジェンシャル面での非点収差量を表している。歪曲収差図において、縦軸は半画角(deg)であり、横軸は歪曲率（％）である。ここでの歪曲収差は殆ど見られない。
【００６５】
以下に、各実施例における条件式の値を示す。なお、表中のG1は、ＧＲＩＮレンズの第１面である事を意味している。

【００６６】

【００６７】

【００６８】

【００６９】

【００７０】
【発明の効果】
以上説明したように、本発明によれば、小型で高性能な光ピックアップレンズを提供する事ができる。さらには軸上色収差や倍率色収差等が良好に補正された光ピックアップレンズを提供する事ができる。
【図面の簡単な説明】
【図１】本発明の光ピックアップレンズの第１の実施形態に対応するレンズ構成図。
【図２】本発明の光ピックアップレンズの第２の実施形態に対応するレンズ構成図。
【図３】本発明の光ピックアップレンズの第３の実施形態に対応するレンズ構成図。
【図４】本発明の光ピックアップレンズの第４の実施形態に対応するレンズ構成図。
【図５】実施例１に対応する収差図。
【図６】実施例２に対応する収差図。
【図７】実施例３に対応する収差図。
【図８】実施例４に対応する収差図。
【符号の説明】
Ｌ 光線
Ｘ 光軸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup lens, and more particularly to an optical pickup lens that is applied to, for example, an optical disk device and performs data recording, reproduction, and erasing using a near-field optical recording technique.
[0002]
[Prior art]
Conventionally, it has been desired to increase the recording density in recording media such as optical disks. In order to improve the recording density, a technique for condensing a light beam minutely is used. For example, the wavelength of laser light to be used is shortened or the numerical aperture of the objective lens is increased. However, since these measures alone have a light diffraction limit, a great improvement in recording density cannot be realized. Thus, so-called near-field optical recording technology has received the most attention for such a demand for higher density.
[0003]
For example, by using a recently proposed SIL (Solid Immersion Lens), it is possible to form a condensing spot that is much smaller than in the air by focusing the condensing spot in a medium having a high refractive index. Specifically, for example, as described in JP-A-11-296889, at least an objective lens and a SIL are provided, and the SIL is formed by a gradient index optical element (hereinafter referred to as GRIN). It is characterized by a high numerical aperture.
[0004]
[Problems to be solved by the invention]
However, in the configuration as described in JP-A-11-296889, since there are a plurality of lenses, there is a problem in miniaturizing the optical head. Further, although there is a description about GRIN, a specific example thereof is not shown.
[0005]
The present invention has been made in view of such a situation, and an object thereof is to provide a small and high-performance optical pickup lens. It is another object of the present invention to provide an optical pickup lens in which axial chromatic aberration, lateral chromatic aberration and the like are well corrected.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises a SIM lens that forms an image of a light beam from a light source in the vicinity of a recording surface using at least one reflection, and the SIM lens is a refraction that satisfies the following conditional expression: It is characterized by comprising a rate distribution type lens.
−3.0 <N ₁ / φ _SIM ² <3.0
However,
N ₁ : secondary refractive index distribution coefficient φ _SIM of the gradient index lens: SIM lens power. here,
N (h) = N ₀ + N ₁ · h ² + N ₂ · h ⁴ + N ₃ · h ⁶ + N ₄ · h ⁸ +
It is. However,
N (h): Refractive index h at the position h of the SIM lens h: Height in the direction perpendicular to the optical axis N ₀ : Refractive index on the optical axis N ₁ , N ₂ , N ₃ , N ₄ ,. Refractive index distribution coefficients of second order, fourth order, sixth order, eighth order,.
[0007]
Further, at least one surface of the SIM lens is an aspherical surface. Furthermore, the aspherical surface satisfies the following conditional expression.
For 0 <h <h _max
−6.0 <(φ _a −φ _0a ) / φ _SIM <5.0
However,
h: height in the lens radial direction h _max : effective lens diameter φ _a : power of local surface of aspheric surface φ _0a : power of surface due to aspherical reference curvature φ _SIM : power of SIM lens, φ _a And φ _0a are expressed by the following equations.
When the aspheric surface is a refractive surface, φ _a = C _alo {N (h) ′ − N (h)}
φ _0a = C ₀ (N ₀ ′ −N ₀ )
When the aspherical surface is a reflection surface φ _a = −2 C _alo N _r (h)
φ _0a = -2C ₀ N _r
However,
C _alo : Local curvature at each height of the aspheric surface C ₀ : Reference curvature N (h) ′ of the aspheric surface: Refractive index N (h) at each height of the aspheric image side medium: Aspheric object refractive index N ₀ at the height of the side medium ': refractive index N ₀ on the optical axis of the aspherical image side medium refractive index on the optical axis of the aspheric object side medium N _r (h): the reflection In the case of an aspherical surface, the refractive index N _r at each height of the medium in which the light ray exists: When the reflecting aspherical surface, it is the refractive index on the optical axis of the medium in which the light ray exists.
[0008]
The SIM lens is characterized in that both surfaces thereof are aspherical.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. In the above-described near-field optical recording technology, a compact and high-performance optical system is desired for an optical pickup for recording, reproducing, and erasing data. A SIM (Solid Immersion Mirror) lens is a suitable lens for increasing the numerical aperture and the optical head in such an optical system.
[0010]
In general, in an optical disc apparatus, when a plurality of types of discs such as a CD (Compact Disc) and a DVD (Digital Versatile Disc) are used, or when a photochromic material is used as a recording medium, for example, recording, reproduction, and erasing are performed. Since it is performed at different wavelengths, it is desirable that the optical system be compatible with multi-wavelength light sources. Accordingly, the SIM lens is required to be a high-performance lens having no chromatic aberration.
[0011]
In the present invention, GRIN is used in order to obtain a high-performance SIM lens free from various aberrations, particularly chromatic aberration. Regarding manufacturing of GRIN, manufacturing of Radial GRIN having a large diameter is very difficult. However, since the SIM lens as an optical pickup lens is required to be downsized, the diameter thereof may be relatively small. Therefore, it can be seen that the GRIN is suitable for the SIM lens in terms of manufacturing.
[0012]
The optical pickup lens of the present invention comprises a SIM lens that forms an image of a light beam from a light source in the vicinity of a recording surface of an optical disk or the like using at least one reflection. The SIM lens is composed of a gradient index lens (GRIN lens), and it is desirable that the following conditional expression is satisfied.
[0013]
^{_{-3.0 <N 1 / φ SIM 2}} <3.0 (1)
However,
N ₁ : secondary refractive index distribution coefficient φ _SIM of the gradient index lens: SIM lens power.
[0014]
here,
N (h) = N ₀ + N ₁ · h ² + N ₂ · h ⁴ + N ₃ · h ⁶ + N ₄ · h ⁸ +
It is. However,
N (h): Refractive index h at the position h of the SIM lens: Height in the direction perpendicular to the optical axis N ₀ : Refractive index on the optical axis N ₁ : Secondary refractive index distribution coefficient N ₂ : 4 Next-order refractive index distribution coefficient N ₃ : 6th-order refractive index distribution coefficient N ₄ : 8th-order refractive index distribution coefficient (hereinafter the same)
It is.
[0015]
Conditional expression (1) is a conditional expression related to the refractive index distribution of the gradient index lens constituting the SIM lens, and is a conditional expression for correcting various aberrations. If it falls outside the range of this conditional expression, correction of the Petzval sum becomes difficult and coma increases, which is not desirable.
[0016]
Further, since at least one surface of the SIM lens is aspherical, the degree of freedom of aberration correction increases, which is desirable in design. At this time, it is desirable that the aspherical surface satisfy the following conditional expression.
[0017]
For 0 <h <h _max
−6.0 <(φ _a −φ _0a ) / φ _SIM <5.0 (2)
However,
h: height in the lens radial direction h _max : lens effective diameter φ _a : power of local surface of aspheric surface φ _0a : power of surface based on aspherical reference curvature φ _SIM : power of SIM lens.
[0018]
Here, φ _a and φ _0a are expressed by the following equations.
When the aspheric surface is a refractive surface, φ _a = C _alo {N (h) ′ − N (h)}
φ _0a = C ₀ (N ₀ ′ −N ₀ )
When the aspherical surface is a reflection surface φ _a = −2 C _alo N _r (h)
φ _0a = -2C ₀ N _r
[0019]
However,
C _alo : Local curvature at each height of the aspheric surface C ₀ : Reference curvature N (h) ′ of the aspheric surface: Refractive index N (h) at each height of the aspheric image side medium: Aspheric object refractive index N ₀ at the height of the side medium ': refractive index N ₀ on the optical axis of the aspherical image side medium refractive index on the optical axis of the aspheric object side medium N _r (h): the reflection In the case of an aspherical surface, the refractive index N _r at each height of the medium in which the light ray exists: When the reflecting aspherical surface, it is the refractive index on the optical axis of the medium in which the light ray exists.
[0020]
Conditional expression (2) is an aspherical conditional expression used for the SIM lens, and is a conditional expression for performing aberration correction. If the aspherical surface deviates from the range of this conditional expression, coma aberration and the like are likely to occur, and if it is attempted to correct it, higher order aberrations often increase, which is not desirable.
[0021]
Further, the SIM lens may be aspheric on both surfaces. This is desirable because the degree of freedom of design is further increased from that of a single-sided aspheric surface.
[0022]
In addition, in the optical pickup lens of the present invention, it is preferable that the following conditional expression is satisfied.
^{_{-5.0 <N 2 / φ SIM 4}} <5.0 (3)
However,
N ₂ : Fourth-order refractive index distribution coefficient φ _SIM of the gradient index lens: SIM lens power.
[0023]
Conditional expression (3) is a conditional expression regarding the refractive index distribution of the gradient index lens constituting the SIM lens, and is a conditional expression for correcting various aberrations. Deviating from the range of this conditional expression is not desirable because the third-order aberration increases, making it difficult to correct each aberration, and in particular increasing coma.
[0024]
Moreover, it is desirable to satisfy the following conditional expressions.
For 0 <H <H _max ,
−0.2 <{ν _d (H) −ν _d (0)} / ν _d (0) ≦ 0.2 (4)
here,
ν _d (H) = {N _d (H) −1} / {N _F (H) −N _C (H)}
However,
ν _d (H): Dispersion value N _d (H) at a point away from the optical axis by a height H in the gradient index lens N _d (H): d-line refractive index N _F (H ): F-line refractive index N _{C at} height H (H): C-line refractive index at height H.
[0025]
Moreover, it is desirable to satisfy the following conditional expressions.
−0.1 <(N ₁ λ−N _1d ) / φ _SIM ² <0.1 (5)
However,
N _1d : Secondary refractive index distribution coefficient for the d-line of the gradient index lens N ₁ λ: Secondary refractive index distribution coefficient for the C-line and F-line of the gradient index lens φ _SIM : With the power of the SIM lens is there.
[0026]
When the SIM lens is composed of a gradient index lens, the gradient index lens also functions to correct chromatic aberration. Conditional expressions (4) and (5) are conditions of dispersion and refractive index distribution coefficient to be satisfied by the gradient index lens when a gradient index lens is used as the SIM lens. When out of range, color correction becomes very difficult due to chromatic aberration occurring in the lens.
[0027]
Moreover, it is desirable to satisfy the following conditional expressions.
−0.2 <φ _M / φ _S <0.5 (6)
However,
φ _S : Power of the surface of the gradient index lens φ _M : Power of the medium of the gradient index lens.
[0028]
Here, φ _S and φ _M are the power of the gradient index lens constituting the SIM lens is φ _SIM .
φ _SIM = φ _S + φ _M
It is represented by φ _S is the power when the lens is a homogeneous lens. Incidentally, the refractive index is the refractive index on the optical axis of the lens.
[0029]
Φ _M is the power of the medium due to the refractive index distribution of the lens,
φ _M = -2N _1d・ T
It is represented by However,
T: SIM lens core thickness N _1d : Secondary refractive index distribution coefficient for the d-line of the gradient index lens.
[0030]
Conditional expression (6) is a condition that the refractive index distribution type lens should satisfy when the SIM lens is composed of a refractive index distribution type lens. If the upper limit of the conditional expression is exceeded, the refractive index distribution becomes too large. This is not desirable because it is difficult to manufacture and high-order aberrations occur. If the lower limit of the conditional expression is not reached, the negative power of the refractive index distribution becomes too large, and the positive power of the surface becomes large, making it difficult to correct the Petzval sum, and correcting each aberration, In particular, it is not desirable because correction of higher-order aberrations becomes difficult.
[0031]
By the way, when the SIM lens is composed of a single gradient index lens, it is desirable that the object side has a plano-convex positive lens shape having a flat surface. As a result, chromatic aberration generated on the lens surface can be almost eliminated, so that the degree of freedom in having a refractive index distribution is increased, and particularly off-axis coma aberration can be reduced.
[0032]
At this time, if a SIM lens is to be constructed without using a gradient index lens, the single-sided aspherical structure with only the convex side surface will have insufficient degree of freedom in aberration correction, and off-axis coma will increase. This is not desirable. In order to prevent this, if a double-sided aspherical structure is used, or if the object side surface is formed as a spherical surface, a problem of chromatic aberration occurs, which is not desirable. Eventually, a gradient index lens is required.
[0033]
1 to 4 are lens configuration diagrams respectively corresponding to the first to fourth embodiments of the optical pickup lens of the present invention. The left side of each figure is the object side (light source side), and the right side is the image side (recording surface side). A surface si (i = 1, 2, 3,...) In the lens configuration diagram is an i-th surface counted from the light source side, and a surface si marked with * is an aspherical surface. Each figure is also an optical path diagram showing the locus of the light beam L from the light source side. X is the optical axis.
[0034]
"Example"
Hereinafter, the structure of the optical pickup lens of the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Examples 1 to 4 listed here correspond to the first to fourth embodiments described above, respectively, and optical configuration diagrams (FIGS. 1 to 4) representing the respective embodiments are the opticals of the corresponding examples. Each configuration is shown. In the construction data of each embodiment, si (i = 1,2,3, ...) is the i-th surface counted from the light source side, and ri (i = 1,2,3, ...) is The radius of curvature of the surface si (mm).
[0035]
Further, di (i = 0, 1, 2, 3,...) Represents the i-th axis upper surface interval (mm) counted from the light source side. In addition, a refractive index and a refractive index distribution coefficient for light of each reference wavelength are separately shown. Here, in each embodiment, the second surface and the third surface are reflection surfaces, the first surface is the same as the third surface, and the second surface is the same as the fourth surface. In each example, a surface si marked with * indicates that the surface is an aspheric surface, and is defined by the following expression representing the aspheric surface shape. Each aspheric data is shown together with other data.
[0036]
X (H) = (C · H ² ) / {1+ (1−ε · C ² · H ² ) ^1/2 } + ΣAi · H ⁱ
However,
H: Height X (H) in the direction perpendicular to the optical axis: Displacement amount in the optical axis direction at the position of height H (based on the surface vertex)
C: paraxial curvature ε: quadratic surface parameter Ai: i-th order aspherical coefficient.
[0037]

[0038]
[Refractive index and refractive index distribution coefficient (d-line)]
N0 = 1.80518
N2 = -8.51778 × 10 ^-3
N4 = 5.34182 × 10 ^-2
N6 = -5.91190 × 10 ^-3
[0039]
[Refractive index and refractive index distribution coefficient (C line)]
N0 = 1.79610
N2 = -8.48217 × 10 ^-3
N4 = 5.32367 × 10 ^-2
N6 = -5.82036 × 10 ^-3
[0040]
[Refractive index and refractive index distribution coefficient (F line)]
N0 = 1.82776
N2 = -8.60387 × 10 ^-3
N4 = 5.38535 × 10 ^-2
N6 = -6.12383 × 10 ^-3
[0041]
[Aspherical data of 1st surface (s1)]
ε = 1
A4 = -1.12666 × 10 ^-2
A6 = -2.54647 × 10 ^-2
A8 = -5.25437 × 10 ^-3
A10 = -3.27467 × 10 ^-3
[0042]
[Aspherical data of 2nd surface (s2)]
ε = 1
A4 = -1.96267 × 10 ^-2
A6 = -2.74829 × 10 ^-3
A8 = -4.96284 × 10 ^-4
A10 = -4.35596 × 10 ^-5
[0043]
[Aspherical data of 3rd surface (s3)]
ε = 1
A4 = 1.12666 × 10 ^-2
A6 = 2.54647 × 10 ^-2
A8 = 5.25437 × 10 ^-3
A10 = 3.27467 × 10 ^-3
[0044]
[Aspherical data of the 4th surface (s4)]
ε = 1
A4 = -1.96267 × 10 ^-2
A6 = -2.74829 × 10 ^-3
A8 = -4.96284 × 10 ^-4
A10 = -4.35596 × 10 ^-5
[0045]

[0046]
[Refractive index and refractive index distribution coefficient (d-line)]
N0 = 1.80518
N2 = -2.15427 × 10 ^-2
N4 = 1.93470 × 10 ^-2
[0047]
[Refractive index and refractive index distribution coefficient (C line)]
N0 = 1.79610
N2 = -2.14399 × 10 ^-2
N4 = 1.92542 × 10 ^-2
[0048]
[Refractive index and refractive index distribution coefficient (F line)]
N0 = 1.82776
N2 = -2.18173 × 10 ^-2
N4 = 1.95936 × 10 ^-2
[0049]
[Aspherical data of 2nd surface (s2)]
ε = 1
A4 = -4.56298 × 10 ^-3
A6 = 1.22155 × 10 ^-5
A8 = 2.30733 × 10 ^-4
A10 = -7.40261 × 10 ^-5
[0050]
[Aspherical data of the 4th surface (s4)]
ε = 1
A4 = -4.56298 × 10 ^-3
A6 = 1.22155 × 10 ^-5
A8 = 2.30733 × 10 ^-4
A10 = -7.40261 × 10 ^-5
[0051]

[0052]
[Refractive index and refractive index distribution coefficient (d-line)]
N0 = 1.80518
N2 = -1.88189 × 10 ^-2
N4 = 3.78850 × 10 ^-2
[0053]
[Refractive index and refractive index distribution coefficient (C line)]
N0 = 1.79610
N2 = -1.87283 × 10 ^-2
N4 = 3.76971 × 10 ^-2
[0054]
[Refractive index and refractive index distribution coefficient (F line)]
N0 = 1.82776
N2 = -1.90597 × 10 ^-2
N4 = 3.83653 × 10 ^-2
[0055]
[Aspherical data of 2nd surface (s2)]
ε = 1
A4 = -1.11176 × 10 ^-2
A6 = 3.42294 × 10 ^-4
A8 = 3.15786 × 10 ^-4
A10 = -9.32458 × 10 ^-5
[0056]
[Aspherical data of the 4th surface (s4)]
ε = 1
A4 = -1.11176 × 10 ^-2
A6 = 3.42294 × 10 ^-4
A8 = 3.15786 × 10 ^-4
A10 = -9.32458 × 10 ^-5
[0057]

[0058]
[Refractive index and refractive index distribution coefficient (d-line)]
N0 = 1.80518
N2 = -1.60621 × 10 ^-2
N4 = 1.88522 × 10 ^-2
N6 = -2.52711 × 10 ^-13
N8 = -1.30901 × 10 ^-18
[0059]
[Refractive index and refractive index distribution coefficient (C line)]
N0 = 1.79610
N2 = -1.63944 × 10 ^-2
N4 = 1.87068 × 10 ^-2
N6 = -4.48542 × 10 ^-13
N8 = -2.60300 × 10 ^-18
[0060]
[Refractive index and refractive index distribution coefficient (F line)]
N0 = 1.82776
N2 = -1.52353 × 10 ^-2
N4 = 1.92167 × 10 ^-2
N6 = -3.25885 × 10 ^-12
N8 = 4.19719 × 10 ^-18
[0061]
[Aspherical data of 1st surface (s1)]
ε = 1
A4 = 1.19299 × 10 ^-2
A6 = -1.74204 × 10 ^-3
A8 = -9.99859 × 10 ^-4
A10 = 3.79001 × 10 ^-4
[0062]
[Aspherical data of 3rd surface (s3)]
ε = 1
A4 = -1.19299 × 10 ^-2
A6 = 1.74204 × 10 ^-3
A8 = 9.99859 × 10 ^-4
A10 = -3.79001 × 10 ^-4
[0063]
FIGS. 5 to 8 are aberration diagrams corresponding to Examples 1 to 4, respectively, showing spherical aberration, astigmatism, and distortion aberration in order from the left. In the spherical aberration diagram, the vertical axis is the value obtained by normalizing the incident height to the recording surface by the maximum height, and the horizontal axis is the focal position (the amount of deviation in the optical axis direction from the paraxial imaging position) (mm ). The solid line C represents the spherical aberration with respect to the C line (wavelength 656.3 nm), the dotted line d represents the spherical aberration with respect to the d line (wavelength 587.6 nm), and the dashed line F represents the F line (wavelength 486.1 nm). Each spherical aberration amount is shown.
[0064]
In the astigmatism diagram, the vertical axis represents the half field angle (deg), and the horizontal axis represents the focal position (the amount of deviation in the optical axis direction from the paraxial imaging position) (mm). A dotted line S represents the amount of astigmatism on the sagittal surface. A two-dot chain line T represents the amount of astigmatism on the tangential surface. In the distortion diagram, the vertical axis represents the half field angle (deg), and the horizontal axis represents the distortion rate (%). Almost no distortion is observed here.
[0065]
The values of conditional expressions in each example are shown below. In the table, G1 means the first surface of the GRIN lens.

[0066]

[0067]

[0068]

[0069]

[0070]
【The invention's effect】
As described above, according to the present invention, a small and high-performance optical pickup lens can be provided. Furthermore, it is possible to provide an optical pickup lens in which axial chromatic aberration, lateral chromatic aberration, and the like are well corrected.
[Brief description of the drawings]
FIG. 1 is a lens configuration diagram corresponding to a first embodiment of an optical pickup lens of the present invention.
FIG. 2 is a lens configuration diagram corresponding to a second embodiment of the optical pickup lens of the present invention.
FIG. 3 is a lens configuration diagram corresponding to a third embodiment of the optical pickup lens of the present invention.
FIG. 4 is a lens configuration diagram corresponding to a fourth embodiment of the optical pickup lens of the present invention.
FIG. 5 is an aberration diagram corresponding to Example 1.
6 is an aberration diagram corresponding to Example 2. FIG.
FIG. 7 is an aberration diagram corresponding to Example 3.
FIG. 8 is an aberration diagram corresponding to Example 4.
[Explanation of symbols]
L Ray X Optical axis

Claims (4)

It comprises a SIM lens that forms an image of light flux from a light source in the vicinity of the recording surface using at least one reflection, and the SIM lens is composed of a gradient index lens that satisfies the following conditional expression: An optical pickup lens;
−3.0 <N ₁ / φ _SIM ² <3.0
However,
N ₁ : secondary refractive index distribution coefficient φ _SIM of the gradient index lens: SIM lens power. here,
N (h) = N ₀ + N ₁ · h ² + N ₂ · h ⁴ + N ₃ · h ⁶ + N ₄ · h ⁸ +
It is. However,
N (h): Refractive index h at the position h of the SIM lens h: Height in the direction perpendicular to the optical axis N ₀ : Refractive index on the optical axis N ₁ , N ₂ , N ₃ , N ₄ ,. Refractive index distribution coefficients of second order, fourth order, sixth order, eighth order,. The optical pickup lens according to claim 1, wherein at least one surface of the SIM lens is an aspherical surface. The optical pickup lens according to claim 2, wherein the aspherical surface satisfies the following conditional expression:
For 0 <h <h _max
−6.0 <(φ _a −φ _0a ) / φ _SIM <5.0
However,
h: height in the lens radial direction h _max : effective lens diameter φ _a : power of local surface of aspheric surface φ _0a : power of surface due to aspherical reference curvature φ _SIM : power of SIM lens, φ _a And φ _0a are expressed by the following equations.
When the aspheric surface is a refractive surface, φ _a = C _alo {N (h) ′ − N (h)}
φ _0a = C ₀ (N ₀ ′ −N ₀ )
When the aspherical surface is a reflection surface φ _a = −2 C _alo N _r (h)
φ _0a = -2C ₀ N _r
However,
C _alo : Local curvature at each height of the aspheric surface C ₀ : Reference curvature N (h) ′ of the aspheric surface: Refractive index N (h) at each height of the aspheric image side medium: Aspheric object refractive index N ₀ at the height of the side medium ': refractive index N ₀ on the optical axis of the aspherical image side medium refractive index on the optical axis of the aspheric object side medium N _r (h): the reflection In the case of an aspherical surface, the refractive index N _r at each height of the medium in which the light ray exists: When the reflecting aspherical surface, it is the refractive index on the optical axis of the medium in which the light ray exists. The optical pickup lens according to claim 1, wherein both sides of the SIM lens are aspherical surfaces.

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