JPH116955A - Optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical system provided with a collimator lens capable of compensating the curvature of field well and especially suitably used in a multibeam scanning optical system where plural laser diodes are set as a light source by providing the optical system with the collimator lens having a refracting surface which is concave toward the light source side. SOLUTION: This optical system uses the light source consisting of plural laser diodes and provided with the collimator lens having the refracting surface which is concave toward the light source side. By arranging the refracting surface which is concave toward the light source side, such lens constitution that luminous flux emitted from the light source and transmitted through the refracting surface is divergent luminous flux and is made collimated light by the succeeding refracting surface having positive power is obtained. As a result, the concave refracting surface is effective to reduce a Petzval's sum and obtain both desired saggital and meridional image surfaces. Then, the optical system is suitable to be used in an optical system recording and reproducing device where plural proximate laser diodes are set as the light source in addition to the multibeam scanning optical system where plural laser diodes are set as the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system using a laser diode array in which a plurality of laser diodes are arranged on a line or a surface close to each other as a light source.

[0002] Used especially in multi-beam scanning optical systems,
The present invention relates to an optical system having a collimator lens for converting a divergent light beam from a semiconductor laser into a substantially parallel light beam, and an optical system of an optical recording / reproducing apparatus using a plurality of laser diodes as light sources.

[0003]

2. Description of the Related Art In laser beam scanning optics for writing in digital copiers and laser beam printers, etc.
Collimates the light beam emitted from the laser diode,
A collimator lens is used to guide the subsequent optics.

[0004] The image plane characteristics required of this collimator lens are rather loose when only one laser diode is used as a light source. That is, since the size of the light source is as small as about several μm, it is sufficient that the angle of view satisfies the angle of view corresponding to the mounting error or the mounting adjustment error of the laser diode or the collimator lens. For example, the angle of view 2ω = 2 ° However, in this case, the entire angle of view of 2 ° is not used at the same time, so the lens position should be adjusted to the best focus position according to the angle of view used due to mounting errors. I just need. Therefore, there is no practical problem if the astigmatism is small even if there is some curvature of field.

On the other hand, in a multi-beam scanning optical system in which writing is performed by a plurality of laser beams, a multi-beam laser diode in which two or more laser diodes are arranged in a line in the sub-scanning direction in proximity to each other is used as a light source. Using an array, multiple emitted light beams
There is known a configuration in which two collimator lenses convert the light into parallel light and guide the light to a subsequent optical system.

Since the collimator lens used in this method is used for a plurality of laser diodes at the same time, it has an angle of view corresponding to the size of the entire light source and has a good focus position at one focus position with respect to the entire angle of view. It is required to have a large aberration. Therefore, in addition to the performance required when one laser diode is used, it is necessary that the field curvature is small.

Also, in an optical system of an optical recording / reproducing apparatus using an optical disk or the like as a medium, a laser diode array in which a plurality of laser diodes are arranged close to each other on a plane is proposed as a light source in order to speed up recording / reproducing. Have been.

[0008] This optical system also has an angle of view covering the entire size of the light source similarly to the above-described collimator lens, and has good aberration with respect to the entire angle of view at one focus position. Required. Therefore, in addition to the performance required when one laser diode is used, it is necessary that the field curvature is small.

[0009]

The angle of view of the collimator lens of the above-mentioned type is, for example, 18 when the light-emitting portion is spaced by 0.1 mm.
Approximately 10 if the collimated lens with a focal length of 10 mm covers the multi-beam laser diode array
° angle of view is required. If the collimator lens has four light emitting units and a focal length of 20 mm, the angle of view may be about 1 °.

An object of the present invention is to provide a collimator lens having an angle of view of about 2ω = 1 ° to 10 ° and having a well-corrected curvature of field, especially a multi-beam scanning optical system using a plurality of laser diodes as light sources. A numerical aperture NA0.
An object of the present invention is to provide an optical system having a collimator lens of about 15 to 0.35.

Another object of the present invention is to provide an optical system which has a well-corrected screen curvature and is suitable for use in an optical recording / reproducing apparatus using a plurality of laser diodes in proximity as light sources and an optical disk or the like as a medium. To provide.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system using a plurality of laser diodes as a light source, wherein the optical system includes a collimator lens having a concave refraction surface facing the light source. The invention according to claim 1) is achieved.

Another object of the present invention is to provide an optical system of an optical recording / reproducing apparatus which uses a plurality of laser diodes adjacent to each other as a light source and forms an image of the light source, wherein the optical system has a concave refraction toward the opposite side of the light source. An optical system having a surface. (An invention according to claim 6) An optical system of an optical recording / reproducing apparatus for forming an image of a light source by using a plurality of laser diodes close to each other as a light source, and having a refracting surface concave toward the light source. An optical system characterized by the above. (Invention according to claim 10) An optical system of an optical recording / reproducing apparatus for forming an image of a light source by using a plurality of laser diodes arranged close to each other on a plane, wherein the plurality of laser diodes An optical system, characterized by having a negative lens that satisfies the following condition: (Invention of Claim 14) 0.2 ≦ | f _S / f _T | ≦ 5.0 (10) 0 ≦ | d _S / f _S | ≦ 1.0 (11) f _S : Focus of this negative lens Distance f _T : Focal length of the whole system excluding this negative lens d _S : Distance between this light source and this negative lens An optical recording / reproducing apparatus that forms an image of this light source by using a plurality of laser diodes that are close to each other as a light source. The optical system according to claim 1, wherein the plurality of laser diodes are arranged on a concave surface concave on the image side, and satisfy the following condition. (Invention according to claim 15) 0 <e / (h 2 f W) ≦ 20 (12) e: a bending amount of the concave surface, measured in the optical axis direction, between the center and the outermost periphery of the light source of the light source Difference in position in the optical axis direction f _W : focal length of the whole system h: half of the maximum size of the light source measured in the vertical direction from the optical axis, that is, half of the diagonal size.

Is achieved by:

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical system according to the present invention has the following configuration and operation.

An optical system according to the present invention is an optical system using a plurality of laser diodes as a light source, and has a collimator lens having a refracting surface concave toward the light source. .

In the present invention, by disposing a collimator lens having a concave refraction surface toward the light source side,
A light beam emitted from the light source and transmitted through this surface is a divergent light beam, and a lens structure that converts the light beam into collimated light can be obtained by a refraction surface having a subsequent positive power. As a result, the concave refracting surface reduces the Petzval sum, which is effective for obtaining desirable sagittal and meridional image planes.

(Structure and Operation of Claim 2) The collimator lens according to the present embodiment is a single collimator lens having a concave refraction surface facing the light source side, wherein the refraction surface on the light source side has the same paraxial curvature. It has an aspherical surface that is displaced closer to the light source than a spherical surface having a radius, and satisfies the following conditions.

0.30 <r ₂ /f<2.0 (1) 0.20 <d / f <1.5 (2) r ₂ : radius of curvature of the refracting surface on the light source side f: focal length d: center Thickness In the above configuration, more desirable conditions for the conditional expressions (1) and (2) are as follows.

0.50 <r ₂ /f<1.50 (1) ′ 0.50 <d / f <1.20 (2) ′ In the present embodiment, the objective is a simple configuration of a single ball. A collimator lens is obtained. By providing an aspherical component displaced toward the light source on the refracting surface on the light source side, astigmatism generated on the opposite surface can be corrected, and a good sagittal and meridional image plane can be obtained.

Conditional expressions (1) and (2): Both are conditions for obtaining an appropriate Petzval sum. If the upper limit of (1) or the lower limit of (2) is not satisfied, the Petzval sum increases. If the lower limit of (1) is not reached, telecentricity deteriorates, which is not desirable for use in a multi-beam laser diode array. If the value exceeds the upper limit of (2), the lens becomes too thick, and the cost is increased when molding with glass or resin.

The collimator lens of the present embodiment is a collimator lens having a concave refraction surface facing the light source side, and two meniscuses having a concave refraction surface facing the light source side. A lens, wherein at least one of the concave refractive surfaces has an aspheric surface that is displaced in a direction closer to the light source on the periphery than a spherical surface having the same paraxial radius of curvature,
The following conditions are satisfied.

0.20 <(d ₁ + d ₃ ) / f <1.8 (3) d ₁ : the center thickness of the lens arranged on the long conjugate side d ₃ : the center thickness of the lens arranged on the short conjugate side f: Focal length In the above configuration, more desirable conditions for the conditional expression (3) are as follows.

0.40 <(d ₁ + d ₃ ) / f <1.20 (3) ′ In the present embodiment, compared with the single ball of claim 2,
By providing two positive lenses, telecentricity can be improved by the positive lens on the light source side. By providing an aspherical component displaced toward the light source on the refracting surface on the light source side, astigmatism generated on the opposite surface can be corrected, and a good sagittal and meridional image plane can be obtained.

Conditional expression (3): A condition for obtaining an appropriate Petzval sum. When the value falls outside the lower limit of (3), the Petzval sum increases. When the value falls outside the upper limit of (3), the lens becomes too thick and the glass becomes too thick. Alternatively, when molding with a resin, the cost becomes high, which is not desirable.

The collimator lens according to the present embodiment is a collimator lens having a concave refraction surface facing the light source side. One or two positive lenses and a negative lens are arranged in order from the long conjugate side. It consists of a lens and a positive lens and satisfies the following conditions.

0.15 <r _x /f<0.70 (4) 0.15 <d _x /f<0.70 (5) r _x : radius of curvature d _x of the refraction surface on the light source side of the negative lens On-axis distance f between the negative lens and the positive lens closest to the light source f: focal length In the above configuration, more desirable conditions for conditional expressions (4) and (5) are as follows.

0.20 <r _x /f<0.33 (4) ′ 0.20 <d _x /f<0.50 (5) ′ In the present embodiment, the target collimator lens is achromatized. Thus, it is possible to obtain a collimator lens that is not affected by a wavelength difference or a wavelength change of the laser diode.

Conditional expression (4): A condition for obtaining an appropriate Petzval sum. When the value exceeds the upper limit, the Petzval sum increases. If the value falls below the lower limit, the sensitivity of the negative lens to eccentricity increases, which is not desirable in manufacturing.

Conditional expression (5): In order to obtain telecentricity, the distance between the negative lens and the positive lens closest to the light source is set in an appropriate range. If the upper and lower limits are deviated, it becomes difficult to obtain telecentricity.

(Structure and Operation of Claim 5) The collimator lens of the present embodiment is characterized in that it is a front stop in which a stop is arranged in a space on a long conjugate side.

According to this embodiment, telecentricity is improved.

(Structure and operation of claim 6) In the optical system of the present embodiment, in the optical system of an optical recording and reproducing apparatus using a plurality of laser diodes close to each other as a light source, a convergent light beam is located at a position closer to the opposite side of the light source. However, by arranging them so as to pass through the concave refraction surface toward the opposite side of the light source, the Petzval sum can be effectively reduced, and a desirable sagittal and meridional image plane can be obtained.

(Structure and Operation of Claim 7) The optical system of this embodiment is the same as the optical system of claim 6, except that the solid immersion lens is used.
(Solid immersion lens). Recently, Solid Imager has been used as a method of using the near-field phenomenon of light for optical recording.
Ssion Lens (hereinafter referred to as SIL) has been developed.

Such an SIL is described, for example, in “O plus
E Vol. 20, no. 2 "New Technology Communication Co., Ltd., pp. 187-192. The SIL propagates to the image plane with the wavelength being the wavelength in the SIL, that is, the value obtained by dividing the wavelength of the light source by the refractive index of the SIL, due to the near-field phenomenon, thereby improving the resolution.

As the SIL, a lens having a shape called a hemispherical lens or a super-hemispherical lens (supersphere) has been proposed. In each case, the image side is a plane close to the image plane so as to cause a near-field phenomenon, and the light source side. Is to arrange the hemisphere so as not to cause spherical aberration and coma.

In the lens system of this embodiment, the SIL
Is effective to reduce the Petzval sum that increases due to the hemisphere of the SIL when is used.

(Configuration and Operation of Claim 8) The configuration of this embodiment is effective for obtaining an optical system having a large numerical aperture NA on the image side.

In the lens system of this embodiment, the concave refracting surface is provided with an aspheric surface displaced toward the light source, thereby correcting astigmatism generated on the opposite surface. , Good sagittal and meridional image planes can be obtained.

Both equations (6) and (7) are conditions for obtaining an appropriate Petzval sum. If the upper limit of (6) or the lower limit of (7) is not satisfied, the Petzval sum increases.
When the value falls outside the lower limit of (6), the sensitivity of the lens surface to decentering error increases, which is not desirable in manufacturing. If the condition (7) is not satisfied, compactness is impaired.

According to the tenth aspect of the present invention, in the lens of the present embodiment, in the optical system of the optical recording / reproducing apparatus using a plurality of laser diodes adjacent to each other as a light source, a divergent light beam is generated at a position close to the light source. By arranging the light to pass through the concave refraction surface toward the light source, the Petzval sum can be effectively reduced, and a desirable sagittal or meridional image surface can be obtained.

(The Structure and Operation of Claim 11) The lens system of this embodiment is effective in reducing the Petzval sum that increases due to the hemispherical surface of the SIL when the SIL is used.

(Configuration and Operation of Claim 12) The configuration of this embodiment is effective for obtaining an optical system having a large numerical aperture NA on the image side.

In the lens system according to the present embodiment, the concave refracting surface is provided with an aspheric surface displaced toward the light source, thereby correcting astigmatism generated on the opposite surface. , Good sagittal and meridional image planes can be obtained.

Both equations (8) and (9) are conditions for obtaining an appropriate Petzval sum, and if the ratio deviates from the upper limit of (8) or the lower limit of (9), the Petzval sum increases.
If the value falls outside the lower limit of (8), the sensitivity of the lens surface to decentering error increases, which is not desirable in manufacturing. Outside the upper limit of (9), the compactness is impaired.

(The Structure and Operation of Claims 14 and 15) The lens system of this embodiment is an optical system of an optical recording / reproducing apparatus using a plurality of laser diodes which are close to each other as a light source.
The light source or the vicinity of the light source is configured to obtain good image plane characteristics.

In the lens system according to the present invention, a negative lens serving as a field flattener is provided near the light source.
The upper and lower limits of the expression (10) indicate a range for obtaining an appropriate Petzval sum. Equation (11) is a condition for the negative lens to work well as a field flattener. If the value exceeds the upper limit, the influence on spherical aberration and the like becomes large, which is not desirable.

In the lens system according to the fifteenth aspect, the light source itself is arranged on a concave surface concave toward the image side. Equation (12) defines the upper limit of the amount of curvature of the concave surface. If the upper limit is deviated, the field curvature will be overcorrected.

The following equation is a desirable range for favorably canceling the Petzval sum of the entire system.

[0050] ^{0.3 ≦ e / (h 2 f} W) ≦ 8.0

[0051]

Examples of the present invention will be described below. Examples 1 to 6 shown below are all collimator lenses of an optical system using a plurality of laser diodes as a light source, and have a refractive surface that is concave toward the light source.

The first and second embodiments have a single ball configuration, and are the second embodiment of the present invention.

The third and fourth embodiments have a two-lens configuration with improved telecentricity, and are the third embodiment of the present invention.

The fifth and sixth embodiments have a configuration of three and four lenses, respectively, in which chromatic aberration has been corrected, and are the fourth embodiment of the present invention.

Examples 1 to 6 shown below have a focal length of 100
However, it is assumed that it is used in a range of about 5 mm to 30 mm. Each surface is described in order from the long conjugate side. The cover glass is a cover glass of the light source.

The aspherical surface is represented by the following equation when the optical axis direction is the x axis and the direction perpendicular to the optical axis is the y axis.

[0057]

(Equation 1)

K: Conical coefficient Ai: Aspherical coefficient Pi: Power coefficient of aspherical coefficient (Example 1)

[0059]

[Table 1]

In the collimator lens of Example 1 shown in the lens sectional view of FIG. 1, r ₂ /f=0.63 d / f = 1.00, and the conditional expressions (1) and (2) in claim 2 are satisfied. Satisfies the conditional expressions (1) ′ and (2) ′. FIG. 2 is an aberration diagram of the first embodiment. Although it is a single ball, the field curvature is well corrected.

(Example 2)

[0062]

[Table 2]

In the collimator lens according to the second embodiment shown in the sectional view of FIG. 3, r ₂ /f=1.45 d / f = 1.11, and the conditional expressions (1) and (2) in claim 2 are satisfied. Satisfies the conditional expressions (1) ′ and (2) ′. FIG. 4 shows an aberration diagram of the second embodiment. Although it is a single ball, the field curvature is well corrected.

(Example 3)

[0065]

[Table 3]

The collimator lens of Example 3 shown in the lens cross-sectional view of FIG. 5 satisfies (d ₁ + d ₃ ) /f=0.47, which satisfies conditional expression (3) in claim 3 and further satisfies conditional expression (3). ) 'Is also satisfied. FIG. 6 shows an aberration diagram of the third embodiment. Telecentricity is good, and field curvature is well corrected.

(Embodiment 4)

[0068]

[Table 4]

The collimator lens of Example 4 shown in the lens sectional view of FIG. 7 satisfies (d ₁ + d ₃ ) /f=0.71, which satisfies the conditional expression (3) in claim 3 and further satisfies the conditional expression (3). ) 'Is also satisfied. FIG. 8 shows an aberration diagram of the fourth embodiment. Telecentricity is good, and field curvature is well corrected.

(Embodiment 5)

[0071]

[Table 5]

The collimator lens of the fifth embodiment shown in the lens sectional view of FIG. 9 satisfies r _x /f=0.27 d _x /f=0.42, and the conditional expressions (4) and (5) according to claim 4 are satisfied. Is satisfied, and conditional expressions (4) ′ and (5) ′ are also satisfied. FIG. 10 shows an aberration diagram of the fifth embodiment. The chromatic aberration is corrected, and the field curvature is well corrected.

(Embodiment 6)

[0074]

[Table 6]

The collimator lens according to the sixth embodiment shown in the sectional view of the lens in FIG. 11 satisfies r _x /f=0.25 d _x /f=0.36, and the conditional expressions (4) and (5) according to claim 4 are satisfied. Is satisfied, and conditional expressions (4) ′ and (5) ′ are also satisfied. FIG. 12 shows an aberration diagram of the sixth embodiment. The chromatic aberration is corrected, and the field curvature is well corrected.

(Embodiment 7)

[0077]

[Table 7]

Embodiment 7 is an embodiment corresponding to claims 6, 7, 8, and 9.

FIG. 13 and FIG. 14 are sectional views of the lens, respectively.
FIG.

In the following embodiments including this embodiment, a plurality of laser diodes are arranged on the object surface.

In this embodiment, a super hemispherical lens (super sphere lens) is placed closest to the image side, and the image planes are arranged close to each other to cause a near-field phenomenon. However, in the lens data table, the image side surface of the super sphere lens is shown. And the image plane were collectively represented as an image plane. The aberration diagram also shows the case where the image field is filled with the medium of the supersphere lens.

In this embodiment, the second lens from the object side is provided with a concave surface that is concave on the image side. A convergent light beam is incident on this concave surface, and the position of the concave surface is closer to the image than between the object and the image.

The values of the conditional expressions are as follows.

R _P / f _P = 0.33 (f _P = 0.425) d _P / f _P = 0.93 (Example 8)

[0085]

[Table 8]

The eighth embodiment is defined as claims 10, 11, 12, and 13.
This is an embodiment corresponding to FIG.

FIGS. 15 and 16 are sectional views of the lens, respectively.
FIG.

In this embodiment, a hemispherical lens is placed closest to the image side, and the image planes are arranged close to each other to cause a near-field phenomenon as in the seventh embodiment. The surface and the surface were collectively represented as an image surface. The aberration diagrams also show the case where the image field is filled with the medium of the hemispherical lens.

In this embodiment, the lens closest to the object is provided with a concave surface that is concave on the object side. A divergent light beam is incident on this concave surface, and the position of the concave surface is closer to the object than between the object and the image.

The values of the conditional expressions are as follows.

| R _Q / f _Q | = 0.62 (r _Q <0) (f _Q = 0.
_{721) d Q / f Q =} 0.99 ( Example 9)

[0092]

[Table 9]

The ninth embodiment is an embodiment corresponding to claim 14.

FIGS. 17 and 18 are sectional views of lenses, respectively.
FIG.

In this embodiment, a negative lens that functions as a field flattener is arranged close to the object plane.

The values of the conditional expressions are as follows.

F _S / f _T = 1.02 (f _S = −0.295, f _T =
0.289) d _S / f _S = 0.17 (Example 10)

[0098]

[Table 10]

Embodiment 10 is an embodiment corresponding to claim 15.

FIGS. 19 and 20 are lens sectional views, respectively.
FIG.

In this embodiment, the object surface is a concave surface concave toward the image side.

The values of the conditional expressions are as follows.

E / (h ² f _W ) = 5.2 (e = 0.157, h = 0.10, f _W = 0.30)

[0104]

According to the present invention (claim 1), an optical system having a collimator lens whose field curvature is well corrected can be obtained. Therefore, an optical system having a collimator lens suitable for using a plurality of laser diodes as a light source. A system can be obtained.

Further, according to the present invention, it is possible to obtain an optical system in which the curvature of field is well corrected, which is suitable for an optical recording / reproducing apparatus using a plurality of laser diodes close to each other as a light source.

In the collimator lens of the second aspect, a single-lens configuration is sufficient and the function can be achieved. In addition to the correction of the curvature, the correction of the chromatic aberration is also performed.

According to the present invention (claim 6), in the optical system of an optical recording / reproducing apparatus using a plurality of laser diodes close to each other as a light source, the Petzval sum can be effectively reduced by the arrangement shown in FIG. Thus, both desirable sagittal and meridional image planes can be obtained.

The lens system according to the seventh aspect is effective for reducing the Petzval sum which increases due to the hemispherical surface of the SIL when the SIL is used. Claim 9 which is effective for obtaining
In Japanese Patent Application Laid-Open No. H10-157, an aspheric surface displaced toward the light source is provided on the concave refraction surface to correct astigmatism generated on the opposite surface.

According to the present invention (Claim 10), in the optical system of an optical recording / reproducing apparatus using a plurality of laser diodes close to each other as a light source, the Petzval sum can be effectively reduced by the arrangement shown in FIG. Thus, both desirable sagittal and meridional image planes can be obtained.

The lens system according to the eleventh aspect is effective for reducing the Petzval sum that increases due to the hemispherical surface of the SIL when the SIL is used. According to the thirteenth aspect, the concave refractive surface is provided with an aspheric surface displaced toward the light source, thereby correcting astigmatism generated on the opposite surface.

According to the present invention (claim 14), in the optical system of an optical recording / reproducing apparatus using a plurality of laser diodes close to each other as a light source, good image surface characteristics can be obtained by the arrangement shown in FIG. .

According to the present invention (claim 15), in the optical system of the optical recording / reproducing apparatus using a plurality of laser diodes close to each other as a light source, good image surface characteristics can be obtained by the arrangement shown in FIG. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIG. 2 is an aberration diagram of the first embodiment.

FIG. 3 is a sectional view of a lens according to a second embodiment.

FIG. 4 is an aberration diagram of the second embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIG. 6 is an aberration diagram of the third embodiment.

FIG. 7 is a sectional view of a lens according to a fourth embodiment.

FIG. 8 is an aberration diagram of the fourth embodiment.

FIG. 9 is a sectional view of a lens according to a fifth embodiment.

FIG. 10 is an aberration diagram of the fifth embodiment.

FIG. 11 is a sectional view of a lens according to a sixth embodiment.

FIG. 12 is an aberration diagram of the sixth embodiment.

FIG. 13 is a sectional view of a lens according to a seventh embodiment.

FIG. 14 is an aberration diagram of the seventh embodiment.

FIG. 15 is a sectional view of a lens according to an eighth embodiment.

FIG. 16 is an aberration diagram of the eighth embodiment.

FIG. 17 is a sectional view of a lens according to a ninth embodiment.

FIG. 18 is an aberration diagram of the ninth embodiment.

FIG. 19 is a lens sectional view of a tenth embodiment.

FIG. 20 is an aberration diagram of the tenth embodiment.

Claims (15)

[Claims] 1. An optical system using a plurality of laser diodes as a light source, comprising: a collimator lens having a refracting surface concave toward the light source. 2. A single collimator lens, wherein a refracting surface on the light source side has an aspheric surface which is displaced closer to the light source than a spherical surface having the same paraxial radius of curvature. 2. The optical system according to claim 1, further comprising a collimator lens that fills. _{0.30 <r 2 /f<2.0 (1)} 0.20 <d / f <1.5 (2) r 2: curvature of the refractive surface of the light source side radius f: the focal length d: center thickness 3. A lens having a refracting surface concave toward the light source side.
A collimator lens comprising at least one meniscus lens, wherein at least one of the concave refraction surfaces has an aspheric surface that is displaced in a direction closer to the light source than a spherical surface having the same paraxial radius of curvature, and satisfies the following conditions. The optical system according to claim 1, further comprising: 0.20 <(d ₁ + d ₃ ) / f <1.8 (3) d ₁ : center thickness of the lens arranged on the long conjugate side d ₃ : center thickness of the lens arranged on the short conjugate side f: focus distance 4. The optical system according to claim 1, further comprising a collimator lens that includes one or two positive lenses, a negative lens, and a positive lens in order from a long conjugate side and satisfies the following condition. 0.15 <r _x /f<0.70 (4) 0.15 <d _x /f<0.70 (5) r _x : radius of curvature of the refracting surface on the light source side of the negative lens d _x : negative lens On-axis distance from the positive lens closest to the light source f: focal length 5. The optical system according to claim 1, wherein the collimator lens is a front stop. 6. An optical system of an optical recording / reproducing apparatus which uses a plurality of laser diodes close to each other as a light source and forms an image of the light source, wherein the optical system has a refracting surface concave toward the opposite side of the light source. An optical system characterized by the above. 7. The optical system includes a first lens system and a second lens system in order from a light source side, wherein the first lens system has a refracting surface that is concave toward an opposite side of the light source. The lens system is a single lens, and a solid immersion lens (Solid Immersion) that utilizes a near-field phenomenon.
7. An optical system according to claim 6, wherein the optical system is (Lens). 8. The optical system according to claim 7, wherein the first lens system includes a plurality of lenses, and a lens farthest from the light source has a refractive surface that is concave toward an opposite side of the light source. 9. The optical system according to claim 8, wherein the concave refracting surface has an aspherical surface which is displaced closer to the light source than the spherical surface having the same paraxial curvature, and satisfies the following condition. _{0.20 ≦ r P / f P ≦} 2.0 (6) 0.20 ≦ d P / f P ≦ 2.0 (7) r P: radius of curvature of the refracting surface of the concave f _P: first lens system Composite focal length d _P : center thickness of the lens farthest from the light source in the first lens system 10. An optical system of an optical recording / reproducing apparatus which uses a plurality of laser diodes adjacent to each other as a light source and forms an image of the light source, wherein the optical system has a refracting surface concave toward the light source. Optical system. 11. The optical system comprises a first lens system and a second lens system in order from the light source side, wherein the first lens system has a refracting surface concave toward the light source, and the second lens system has A single lens, a solid immersion lens (Solid Immersion Le
The optical system according to claim 10, wherein ns). 12. The optical system includes a plurality of lenses,
11. The optical system according to claim 10, wherein the lens closest to the light source is a positive lens having a refractive surface that is concave toward the light source. 13. The method according to claim 1, wherein the concave refracting surface has an aspheric surface displaced closer to the light source than the spherical surface having the same paraxial curvature, and satisfies the following condition. 13. The optical system according to 12. 0.30 ≦ | r _Q / f _Q | ≦ 3.0 (r _Q <0) (8) 0.20 ≦ d _Q / f _Q ≦ 2.0 (9) r _Q : radius of curvature f _{Q of} this concave surface : Focal length of the lens closest to the light source d _Q : center thickness of the lens closest to the light source 14. An optical system of an optical recording / reproducing apparatus that uses a plurality of laser diodes arranged in close proximity on a plane as a light source and forms an image of the light source. An optical system comprising a negative lens satisfying the following conditions. 0.2 ≦ | f _S / f _T | ≦ 5.0 (10) 0 ≦ | d _S / f _S | ≦ 1.0 (11) f _S : focal length of this negative lens f _T : this negative lens Focal length of the whole system excluding d _S : distance between this light source and this negative lens 15. An optical system of an optical recording / reproducing apparatus that uses a plurality of adjacent laser diodes as a light source and forms an image of the light source, wherein the plurality of laser diodes are:
An optical system which is arranged on a concave surface concave on the image side and satisfies the following conditions. ^{0 <e / (h 2 f} W) ≦ 20 (12) e: a bending amount of the concave surface, measured in the direction of the optical axis, the difference f a position in the optical axis direction between the center and the outermost periphery of the light source of the light source _W : focal length of the whole system h: half of the maximum size of the light source measured in the vertical direction from the optical axis, that is, half of the diagonal size.