JP4250870B2 - Catadioptric objective lens - Google Patents

Description

【００２５】
[第１面(S1)の非球面データ]
K= 0.000000,A1=-1.0000×10^-2,A4=-2.1471,A6= 2.4423×10,A8=-1.4287×10²,A10= 3.1415×10²
[第３面(S3)の非球面データ]
K=-1.289458,A4= 0.165969×10^-2,A6= 0.852087×10^-4,A8=-0.230396×10^-4,A10= 0.334107×10^-5
【００２６】
《実施例２》

【００２７】
[第１面(S1)の非球面データ]
K= 0.000000,A1=-1.2000×10^-2,A4=-1.3392,A6= 3.3416×10,A8=-2.3219×10²,A10= 5.2609×10²
[第３面(S3)の非球面データ]
K=-0.161338,A4= 0.488687×10^-2,A6=-0.755868×10^-2,A8= 0.396075×10^-2,A10=-0.706527×10^-3
【００２８】
【発明の効果】
以上説明したように本発明によれば、入射光量を高い効率で利用することが可能な反射屈折対物レンズを実現することができる。そして、本発明に係る反射屈折対物レンズを光ピックアップ装置(光情報の記録装置，再生装置，記録再生装置等)に使用すれば、光学記録媒体(光ディスク等)の高密度化に寄与することができる。
【図面の簡単な説明】
【図１】第１の実施の形態(実施例１)の光学構成図。
【図２】実施例１の収差図。
【図３】第２の実施の形態(実施例２)の光学構成図。
【図４】実施例２の収差図。
【符号の説明】
S1 …第１面
S2 …第２面
S3 …第３面
S4 …第４面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catadioptric objective lens. For example, the present invention relates to a catadioptric objective lens for an optical pickup mounted in an optical information recording apparatus, reproducing apparatus, recording / reproducing apparatus, or the like.
[0002]
[Prior art]
In the recent situation where the density of optical disks is increased, it is indispensable to increase the numerical aperture of an objective lens used for an optical pickup. However, when the numerical aperture (NA) becomes 0.8 or more, it is impossible to configure the objective lens only with the refractive power of one lens. This is because the angle between the normal of the surface at the effective diameter position and the optical axis is 45 ° or more, which makes processing difficult and increases error sensitivity. However, when the objective lens is composed of one lens, the number of parts is reduced and the assembling cost is reduced as compared with the case where the objective lens is composed of two or more lenses. Therefore, an objective lens having a single lens structure is desired.
[0003]
If the objective lens is constituted by a cata-dioptric system, it is possible to work for four surfaces with one lens. Such objective lenses have been proposed for near-field use in Japanese Patent Application Laid-Open Nos. 12-99990, 12-113484, etc., and a first refracting surface having a concave refractive surface on the light source side in order of the optical path from the light source side. A second surface formed of a reflection plane, a third surface formed of a reflection surface concave on the image side, and a fourth surface formed of a transmission plane.
[0004]
[Problems to be solved by the invention]
In the objective lens proposed in Japanese Patent Laid-Open Nos. 12-99990, 12-113484, etc., the first surface is constituted by a spherical surface, or an ordinary aspheric surface (that is, an aspheric coefficient of second or higher order). It is thought that it is composed of an aspheric surface defined by For this reason, the central portion of the light beam transmitted through the first surface is transmitted through the fourth surface without being reflected by the second surface, or the central portion of the light beam reflected by the second surface is not reflected by the third surface. One surface is transmitted. As a result, the usable effective light beam has a donut shape with a central portion missing. As the numerical aperture (NA) increases, the area ratio of the hollows in the luminous flux increases. If the incident light quantity is not sufficient, the light quantity becomes insufficient. For example, when the numerical aperture (NA) is 0.8 or more, the hollow diameter is larger than half of the outer diameter, and the available light quantity is about 75% or less of the incident light quantity.
[0005]
The present invention has been made in view of such a situation, and an object of the present invention is to provide a catadioptric objective lens that can use incident light quantity with high efficiency.
[0006]
[Means for Solving the Problems]
To achieve the above object, a catadioptric objective lens according to a first aspect of the present invention includes a first surface composed of a refracting surface having a diverging action, a second surface composed of a reflecting surface, and the first surface in order of the optical path from the light source side. A catadioptric objective lens having a third surface made of a reflective surface in the vicinity of a surface and having a converging action; and a fourth surface made of a transmissive surface in the vicinity of the second surface, wherein the first surface is It consists of an aspherical surface defined by the following formula (AS), and its primary aspherical coefficient A1 satisfies the following conditional expression (1).
x = (C ・ y ² ) / [1+ {1- (1 + K) ・ C ²・ y ² } ^1/2 ] + Σ (Ai ・ y ⁱ )… (AS)
-0.1 <A1 <0.0… ▲ 1 ▼
However,
x: Amount of displacement in the optical axis direction from the reference plane at the position of height y,
y: height perpendicular to the optical axis,
C: curvature at the top of the surface,
K: conic constant,
Ai: i-th order aspheric coefficient,
Σ: sum of i
It is.
[0007]
A catadioptric objective lens according to a second invention is characterized in that, in the configuration of the first invention, the second surface and the fourth surface are formed on the same surface.
[0008]
A catadioptric objective lens according to a third aspect of the present invention is characterized in that, in the configuration of the first or second aspect, a working distance from the fourth surface to the imaging point is equal to or less than a working wavelength.
[0009]
A catadioptric objective lens according to a fourth invention is characterized in that, in the configuration of any one of the first to third inventions, the fourth surface is a flat surface or a convex surface.
[0010]
The catadioptric objective lens of the fifth invention is characterized in that, in the configuration of any one of the first to fourth inventions, the following conditional expression (1) 'is further satisfied.
-0.05 <A1 <-0.0001… ▲ 1 ▼ '
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A catadioptric objective lens embodying the present invention will be described below with reference to the drawings. 1 and 3 are optical configuration diagrams of catadioptric objective lenses corresponding to the first and second embodiments, respectively. In the optical configuration diagram, the surface with Si (i = 1, 2, ...) is the i-th surface counted from the light source side in the order of the optical path, and the surface with Si is marked with an aspherical surface. is there. These catadioptric objective lenses are objective lenses for optical pickups that read and write information by condensing a light beam from a light source onto an optical recording medium such as an optical disk, and form an image from the fourth surface (S4). The optical configuration for the near field whose working distance to the point is equal to or less than the use wavelength. Each objective lens is composed of one lens. The first surface (S1) and the third surface (S3) are located on the light source side, and the second surface (S2) is located on the image side. The fourth surface (S4) is located.
[0012]
Each objective lens is in the vicinity of the first surface (S1) composed of a diverging refracting surface, the second surface (S2) composed of a reflecting surface, and the first surface (S1) in the order of the optical path from the light source side. It has a third surface (S3) composed of a reflecting surface having a converging action, and a fourth surface (S4) composed of a transmitting surface in the vicinity of the second surface (S2), and an incident light beam (collimated light). Is reflected on the second surface (S2) and the third surface (S3) so that the image is reflected in the near field {that is, near the fourth surface (4)} after being reflected twice inside the lens. . Therefore, the light beam from the light source diverges by refraction at the first surface (S1), which is a concave surface, is reflected at the second surface (S2), is condensed by reflection at the third surface (S3), and the fourth surface. The image is formed on the optical recording surface almost simultaneously with the transmission in (S4).
[0013]
As described above, when the objective lens is configured by a catadioptric system, the usable effective light beam has a donut shape with a central portion missing. In general, the larger the numerical aperture (NA), the larger the hollow portion of the light beam, so that the amount of light that can be used effectively becomes extremely small. Therefore, in the objective lens according to each embodiment, the first surface (S1) is composed of an aspherical surface defined by the following formula (AS), and the first-order aspherical coefficient (A1) is The configuration satisfies the conditional expression (1).
[0014]
x = (C ・ y ² ) / [1+ {1- (1 + K) ・ C ²・ y ² } ^1/2 ] + Σ (Ai ・ y ⁱ )… (AS)
-0.1 <A1 <0.0… ▲ 1 ▼
However,
x: Amount of displacement in the optical axis (AX) direction from the reference plane at the position of height y,
y: height perpendicular to the optical axis (AX),
C: curvature at the top of the surface,
K: conic constant,
Ai: i-th order aspheric coefficient,
Σ: sum of i
It is.
[0015]
If the first surface (S1) on which the light beam first enters is an aspherical surface using the first order aspherical coefficient (A1) (ie, a conical aspherical surface with a deformed conical shape), the vicinity of the optical axis (AX) Can be spread outward rapidly. In other words, by setting the first-order aspheric coefficient (A1) to a value smaller than zero, the light beam near the optical axis (AX) is more diverged than the surroundings (the state where there is no central portion of the light beam). be able to. As a result, the portion of the light beam that is not used is reduced, so that the amount of light that can be practically used is about 85% of the amount of incident light even if the hollow area is the same. However, if the degree of cone is high, it is difficult to correct aberrations. Therefore, in each embodiment, satisfactory optical performance is maintained by satisfying conditional expression (1). Although it is difficult to understand in the optical configuration diagram, the apex of the first surface (S1) has a slightly pointed shape.
[0016]
If the first order aspherical coefficient (A1) becomes smaller than the lower limit of conditional expression (1), the spherical aberration near the optical axis (AX) will suddenly fall under, and higher order aspherical coefficients will be used. However, it is difficult to set the spherical aberration in the range of use straight. As a result, the optical performance required for the objective lens cannot be obtained. If the first order aspherical coefficient (A1) increases beyond the upper limit of conditional expression (1), the first surface (S1) becomes the same as the spherical surface, and thus the effect of effectively using the light amount is lost. Thus, it is desirable to satisfy the conditional expression (1) in order to maintain good optical performance, and it is more desirable to satisfy the following conditional expression (1) '.
-0.05 <A1 <-0.0001… ▲ 1 ▼ '
[0017]
In order to simplify the production of the objective lens, it is desirable that the second surface (S2) and the fourth surface (S4) are configured as the same surface as in each embodiment. An optical pickup objective lens is desired to have a small outer diameter. However, if the central portion and the peripheral portion are configured to be different on a small surface, the processing becomes very difficult. If the second surface (S2) and the fourth surface (S4) are formed on the same surface, manufacturing can be facilitated.
[0018]
As described above, in any of the embodiments, the working distance from the fourth surface (S4) to the imaging point is equal to or less than the use wavelength. If the working distance is less than the working wavelength, near-field light can be used, and an objective lens having a numerical aperture (NA) of 1.0 or more may be realized. At this time, if the first-order aspherical coefficient (A1) of the first surface (S1) is set to zero or less in order to effectively use the light beam, the light utilization efficiency is improved even with a high numerical aperture.
[0019]
In any of the embodiments, the fourth surface (S4) is a flat surface. However, when using near-field light, the fourth surface (S4), which is the exit surface of the objective lens, is preferably a convex surface. . In order to use near-field light, the exit surface of the objective lens must be brought close to the surface of the optical recording medium (such as an optical disk) so that there is an air gap equal to or less than the wavelength used. At this time, if there is a lens holding error or a slight tilt of the optical disk, the objective lens having a flat exit surface may damage the surface of the optical recording medium. Since the fourth surface (S4) does not contribute to the imaging action, it does not need to be a convex surface for aberration correction. Therefore, by devising the shape of the fourth surface (S4), it is possible to make the optical pickup easier to use.
[0020]
The objective lens may be configured by a catadioptric system including two or more optical elements by providing at least one of the first to fourth surfaces (S1 to S4) described above as a separate member. However, in practice, it is desirable to configure the objective lens with a single optical element in terms of size, cost, alignment, and the like.
[0021]
【Example】
Hereinafter, the catadioptric objective lens embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 and 2 listed below correspond respectively to the first and second embodiments described above, and optical configuration diagrams (FIGS. 1 and 3) representing the first and second embodiments are as follows. The lens shapes and optical paths of the corresponding Examples 1 and 2 are shown.
[0022]
In the construction data of each example, Si (i = 1, 2,...) Is the i-th surface counted in the order of the optical path from the light source side, and Ri (i = 1, 2,...) Is the curvature of the surface Si. Radius (mm), Di (i = 0,1,2, ...) indicates the i-th axis top surface distance (mm) counted from the light source side in the order of the optical path (D4: working distance), Ni (i = 1, 2,...) Represents the refractive index of the optical material (glass in each example) after the surface Si at the used wavelength λ. The surface Si marked with * indicates that the surface is an aspheric surface, and is defined by the formula (AS) representing the aspheric surface shape. The operating wavelength λ (nm), the numerical aperture NA, the focal length FL (mm), and the aspheric data of each aspheric surface are shown together with other data.
[0023]
2 and 4 show the spherical aberration (units of mm on the horizontal axis: 1.00 on the vertical axis corresponds to NA) in Examples 1 and 2, respectively. Since only the annular luminous flux is used, the hatched portion of 1/3 to 1/2 in the aberration diagram is not related to the focused spot. In Examples 1 and 2, by making the first-order aspherical coefficient (A1) of the first surface (S1) smaller than zero, it is possible to use 85% or more of the incident light flux.
[0024]
Example 1

[0025]
[Aspherical data of the first surface (S1)]
K = 0.000000, A1 = -1.0000 × 10 ^-2 , A4 = -2.1471, A6 = 2.4423 × 10, A8 = -1.4287 × 10 ² , A10 = 3.1415 × 10 ²
[Aspherical data of 3rd surface (S3)]
K = -1.289458, A4 = 0.165969 × 10 ^-2 , A6 = 0.852087 × 10 ^-4 , A8 = -0.230396 × 10 ^-4 , A10 = 0.334107 × 10 ^-5
[0026]
Example 2

[0027]
[Aspherical data of the first surface (S1)]
K = 0.000000, A1 = -1.2000 × 10 ^-2 , A4 = -1.3392, A6 = 3.3416 × 10, A8 = -2.3219 × 10 ² , A10 = 5.2609 × 10 ²
[Aspherical data of 3rd surface (S3)]
K = -0.161338, A4 = 0.488687 × 10 ^-2 , A6 = -0.755868 × 10 ^-2 , A8 = 0.396075 × 10 ^-2 , A10 = -0.706527 × 10 ^-3
[0028]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a catadioptric objective lens that can use the amount of incident light with high efficiency. If the catadioptric objective lens according to the present invention is used in an optical pickup device (optical information recording device, reproducing device, recording / reproducing device, etc.), it can contribute to higher density of an optical recording medium (optical disc, etc.). it can.
[Brief description of the drawings]
FIG. 1 is an optical configuration diagram of the first mode for embodying the present invention (embodiment 1);
2 is an aberration diagram of Example 1. FIG.
FIG. 3 is an optical configuration diagram of the second mode for embodying the present invention (embodiment 2);
FIG. 4 is an aberration diagram of Example 2.
[Explanation of symbols]
S1 ... 1st page
S2 ... the second side
S3 ... Third surface
S4 ... 4th page

Claims (5)

In order of the optical path from the light source side, a first surface composed of a refracting surface having a diverging action, a second surface comprising a reflecting surface, a third surface comprising a reflecting surface in the vicinity of the first surface and having a converging action, A catadioptric objective lens having a fourth surface in the vicinity of the second surface and comprising a transmission surface,
The catadioptric objective is characterized in that the first surface is composed of an aspherical surface defined by the following formula (AS), and the first-order aspherical coefficient A1 satisfies the following conditional expression (1). lens;
x = (C ・ y ² ) / [1+ {1- (1 + K) ・ C ²・ y ² } ^1/2 ] + Σ (Ai ・ y ⁱ )… (AS)
-0.1 <A1 <0.0… ▲ 1 ▼
However,
x: Amount of displacement in the optical axis direction from the reference plane at the position of height y,
y: height perpendicular to the optical axis,
C: curvature at the top of the surface,
K: conic constant,
Ai: i-th order aspheric coefficient,
Σ: sum of i
It is. 2. The catadioptric objective lens according to claim 1, wherein the second surface and the fourth surface are the same surface. The catadioptric objective lens according to claim 1, wherein a working distance from the fourth surface to the imaging point is equal to or less than a working wavelength. The catadioptric objective lens according to claim 1, wherein the fourth surface is a flat surface or a convex surface. 5. The catadioptric objective lens according to claim 1, further satisfying the following conditional expression (1).
-0.05 <A1 <-0.0001… ▲ 1 ▼ '

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