JPH06331888A - Aspherical collimator lens - Google Patents

Abstract

PURPOSE:To provide the practical lens which is an ellipsoidal surface of revolution with the surface on the parallel light exit side having a positive refracting power and consists of the elliptic surface of revolution relatively easy to produce and a spherical surface by expressing the elliptic surface of revolution with a specific formula and has the spherical aberration and the sine condition satisfactorily corrected in the extent of N.A.=0.15 to 0.35 and has a diffraction limit. CONSTITUTION:The surface on the parallel ray exit side is the ellipsoidal surface or revolution having a positive refracting power, and the elliptic surface of revolution is expressed by the formula where X is the distance from a point on the aspherical surface to the tangential surface at the apex of the aspherical surface and (h) is the height from the optical axis and C1 is the curvature of the apex of the ellipsoid and K is a conic coefficient. Further, 0.22<d/f<0.35 and 0.15<N.A.<0.35 are satisfied where (d) is the thickness in the center of the lens and (f) is the focal length of the lens and N.A. is the numerical aperture of the lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a collimator lens for collimating a semiconductor laser light source of a writing optical system such as a magneto-optical disk or a mini disk and a pickup optical system, and more particularly to a collimator lens having an aspherical surface. .

[0002]

2. Description of the Related Art In a reproducing optical system for a compact disc player or a video disc player, a type in which a semiconductor laser is used as a light source and a collimator lens is used for collimating light, a conventional NA has a diffraction limit performance of about 0.12 to 0.2. Is required.

Japanese Patent Publication No. 3-59407 can be cited as an example of a collimator lens conventionally devised for such a purpose. In this conventional example, as in the present invention, the surface on the parallel light exit side is composed of a spheroidal surface having a positive refractive power.

On the other hand, in the objective lens used in the same reproducing optical system, for example, JP-A-61-2117 and JP-A-60-25 are used.
As in No. 0320, an aspherical single lens having a single-sided aspherical surface and diffraction-limited performance has been proposed.

[0005]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 3-59407
Looking at the examples, many of them have NA = 0.14,
Although there is an example of NA = 0.20, the sine condition is worsened because the center thickness of the lens is thin.

Further, JP-A-61-2117 and JP-A-60-250320
The issue is that the aspherical surface used for these is different from the present invention, and is a complicated aspherical shape with an aspherical coefficient.
It is difficult to measure this with high accuracy, which hinders the practical use of the lens. Moreover, these conventional examples are NA.
= 0.4 to 0.5, which is different from the present invention.

The present invention is mainly used in a pickup optical system including a writing optical system such as a magneto-optical disk and a mini disk, which is composed of a spheroidal surface and a spherical surface which are relatively easy to manufacture. The objective of the present invention is to obtain a practical aspherical collimator lens having a diffraction limit in which spherical aberration and sine conditions are well corrected at about 0.35.

[0008]

The above object is to provide a spheroid having a positive refracting power on the surface on the parallel light exit side, wherein the spheroid is X: an aspherical vertex contact point of points on the aspherical surface. Distance from plane, h: height from optical axis, C ₁ : curvature of elliptical vertex,
K: conic coefficient,

[0009]

[Equation 2]

0.22 <d / f <0.35 ··· (1) 0.15 <NA. <0.35 ··· (2) where d: lens center thickness, f: lens' Focal length,
NA: Numerical aperture of the lens, which is achieved by an aspherical collimator lens.

[0011]

The surface on the exit side of the parallel light is a spheroid having a positive refractive power, and the spheroid is represented by the above formula.

In the conditional expression (1), if the lower limit is exceeded, the sine condition becomes worse. On the other hand, if the upper limit is exceeded, the thickness becomes thicker, which makes manufacturing difficult and the back focus becomes short.

Conditional expression (2) is necessary for a collimator lens for a magneto-optical disk or a mini disk. If the lower limit is exceeded, the power from the semiconductor laser of the light source cannot be sufficiently secured, and if the upper limit is exceeded, spherical aberration is exceeded. It becomes difficult to maintain the diffraction-limited performance by maintaining the balance between the sine condition and the sine condition.

[0014]

EXAMPLES Examples according to the present invention will be shown below.

The following symbols are as follows: r ₁ : radius of curvature of surface on parallel light exit side r ₂ : radius of curvature of surface on light source light entrance side d: lens thickness n: refractive index of lens d _c : on light source light entrance side, It is the thickness of the cover glass inserted vertically to the optical axis (refractive index 1.51062).

[0016] Example 1 f = 11.0 N.A. = 0.20 d c = 0.3 r 1 = 6.893 r 2 = -78.153 d = 2.6 n = 1.5824 FIGS sectional view of the conical coefficient K = -0.69166 Example 1 1 ( Fig. 1 (b) shows the aberration diagram in a).
Shown in.

FIG. A cross-sectional view of an embodiment 2 f = 11.0 N.A. = 0.30 d c = 0.3 r 1 = 6.833 r 2 = -88.311 d = 2.6 n = 1.5824 conic constant K = -0.68792 Example 2 2 (a) shows an aberration diagram in FIG. 2 (b).
Shown in.

[0018] Example 3 f = 11.0 N.A. = 0.20 d c = 0.3 r 1 = 6.997 r 2 = -62.753 d = 3.3 n = 1.5824 FIGS sectional view of the conical coefficient K = -0.70860 Example 3 3 ( FIG. 3B is an aberration diagram in FIG.
Shown in.

[0019] Example 4 f = 11.0 N.A. = 0.20 d c = 0.3 r 1 = 6.506 r 2 = -27.039 d = 3.3 n = 1.49275 Fig sectional view of the conical coefficient K = -0.85835 Example 4 4 ( Fig. 4 (b) shows the aberration diagram in a).
Shown in.

[0020] The cross-sectional view of an embodiment 5 f = 11.0 N.A. = 0.20 d c = 0.3 r 1 = 6.377 r 2 = -31.265 d = 2.6 n = 1.49275 conic constant K = -0.82314 Example 5 5 ( FIG. 5B is an aberration diagram in FIG.
Shown in.

[0021]

According to the present invention, a collimator lens for collimating a semiconductor laser light source or the like used in a pickup optical system mainly including a writing optical system such as a magneto-optical disk and a mini disk can be rotated relatively easily. A practical aspherical collimator lens having an ellipsoidal surface and a spherical surface, and having a NA of about 0.15 to 0.35, which is well corrected for spherical aberration and sine conditions, has a diffraction limit.

[Brief description of drawings]

FIG. 1 is a sectional view and an aberration diagram of a lens of Example 1 according to the present invention.

FIG. 2 is a sectional view and an aberration diagram of a lens of Example 2 according to the present invention.

FIG. 3 is a sectional view and an aberration diagram of a lens of Example 3 according to the present invention.

FIG. 4 is a sectional view and an aberration diagram of a lens of Example 4 according to the present invention.

FIG. 5 is a sectional view and an aberration diagram of a lens of Example 5 according to the present invention.

Claims (1)

[Claims] 1. A surface on the parallel light emission side is a spheroid having a positive refractive power, and the spheroid is: X: a distance of a point on an aspherical surface from a tangent plane of an aspherical surface vertex: h: optical axis Height from C ₁ : Curvature of ellipsoidal vertex K: Conic coefficient, 0.22 <d / f <0.35 0.15 <NA. <0.35 where d is the center thickness of the lens f is the focal length of the lens NA is the numerical aperture of the lens Aspherical collimator lens.