JPH07128616A - Aspherical collimator lens - Google Patents

Abstract

PURPOSE:To provide the collimator lens which collimates a semiconductor laser beam source, etc., to parallel beams with a pickup optical system having writing of a magneto-optical disk, minidisk, CD-R, etc., and is good in aberration correction. CONSTITUTION:This aspherical collimator lens emits the parallel beams, consists of aspherical faces on both faces and satisfies 0.75<d/f<0.95, -0.35<r1/r2<-0.22, 0.30<N.A.<0.40, where d: the central thickness of the lens, f: the focal length of the lens, r1: the radius of curvature of the refraction surface on the emit side of the parallel beams, r2 the radius of curvature of the refraction face on a light source side, N.A.: the numerical aperture on the light source side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup optical system for writing a magneto-optical disc, a mini disc, a CD-R or the like, and relates to an aspherical collimator lens for collimating a semiconductor laser light source.

[0002]

2. Description of the Related Art Conventionally, as a known example of an aspherical single lens having a specification of about NAO35 and being used for an optical disc or the like and having good aberration correction, there is JP-A-2-508816, and an example of NA is slightly different. However, as a similar known example, JP-A-2-39
There are JP-A No. 010 and JP-A No. 61-2117.

The aspherical single lens proposed in the related art has a relatively thin lens thickness, and the sine condition is slightly inferior in terms of lens design, so that the off-axis performance is deteriorated.

Further, when it is attempted to realize the aspherical lens by a glass mold lens, if the wall thickness is thin, it may be disadvantageous in terms of molding cost.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to provide a single-lens collimator lens which solves the problems in the above-mentioned proposal, and can be used in magneto-optical discs, mini-discs, CD-R, etc. It is an object of the present invention to provide a collimator lens which is a thicker lens than a conventional one, which is a pickup optical system having writing, and which uses a semiconductor laser light source or the like as parallel light, and which is excellent in aberration correction.

[0006]

According to the present invention, collimated light is emitted and both surfaces are aspherical, and 0.75 <d / f <0.95 ----- -0.35 <r ₁ / r ₂ <-0.22- --- 0.30 <NA. <0.40 ----- However, d: lens center thickness f: lens focal length r ₁ : radius of curvature of the refracting surface on the parallel light exit side r ₂ : refraction on the light source side Surface curvature radius NA: Aspherical collimator lens characterized by satisfying the numerical aperture on the light source side.

[0007]

The conditional expressions (1) to (3) of the present invention are as follows.

The conditional expression relates to the wall thickness of the lens, and if the lower limit is exceeded, the sine condition deteriorates and the off-axis performance deteriorates. Further, glass molding has a disadvantage in terms of molding cost. On the other hand, if the upper limit is exceeded, the wall becomes too thick, which is disadvantageous for molding, and the W. D. (Working distance)
Will be difficult to secure.

The conditional expression relates to the bending of the lens, and if the lower limit is exceeded, the off-axis performance is deteriorated, and if the upper limit is exceeded, the decentering sensitivity of the lens becomes high, and manufacturing becomes difficult.

The conditional expression relates to the numerical aperture of the lens on the light source side. If the lower limit is exceeded, the power for collecting the power of the light source becomes weak. If the upper limit is exceeded, aberration correction becomes difficult and the objective lens is combined. In this case, the vertical magnification becomes large in the correspondence between the light source and the focus of the objective lens,
The collimator lens is easily affected by the focus shift.

Further, in the present invention, it is desirable that 50 <νd <70 (where νd: Abbe number of the lens material) is satisfied as a condition regarding the chromatic dispersion of the lens material. If the lower limit of this conditional expression is exceeded, the focal position shift due to axial chromatic aberration becomes large, and if the upper limit is exceeded, molding of the lens material becomes difficult and the cost becomes high.

[0012]

EXAMPLES Examples of the present invention will be shown below. The symbols in the table represent the following.

R: radius of curvature of refracting surface d: surface spacing n: refractive index of main wavelength of lens material (main wavelength: 790 nm) νd: Abbe number of lens material f: focal length NA: numerical aperture ω: half angle of view Also, the aspherical surface is

[0014]

[Equation 1]

It is represented by.

(Example 1) Table 1 shows lens data of Example 1. Further, FIG. 1 shows a sectional view thereof, and FIG. 2 shows an aberration diagram thereof.

[0017]

[Table 1]

Example 2 Table 2 shows lens data of Example 2. Further, FIG. 3 shows a sectional view thereof, and FIG. 4 shows an aberration diagram.

[0019]

[Table 2]

(Example 3) Table 3 shows lens data of Example 3. Further, FIG. 5 shows a sectional view thereof, and FIG. 6 shows an aberration diagram.

[0021]

[Table 3]

Examples 1 to 3 above are conditional expressions of the present invention.
Is the following value.

[0023]

[Table 4]

[0024]

The collimator lens of the present invention in which the lens thickness is thicker than that proposed in the past is excellent in the sine condition and is excellent in the off-axis performance. Further, the aspherical collimator lens of the present invention has an appropriate thickness, which is advantageous in glass molding.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is an aberration diagram of Example 1 of the present invention.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is an aberration diagram for Example 2 of the present invention.

FIG. 5 is a sectional view of a third embodiment of the present invention.

FIG. 6 is an aberration diagram for Example 3 of the present invention.

Claims (1)

[Claims] 1. Collimated light is emitted and is composed of aspherical surfaces on both sides. 0.75 <d / f <0.95 −0.35 <r ₁ / r ₂ <−0.22 0.30 <NA. Thickness f: focal length of lens r ₁ : radius of curvature of refracting surface on parallel light exit side r ₂ : radius of curvature of refracting surface on light source side NA: aspherical collimator lens characterized by satisfying numerical aperture on light source side .