JPH06215409A - Optical system and chromatic aberration compensating element for optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain the optical system of an optical information recording/ reproducing device in which chromatic aberration is excellently compensated without increasing a number of optical elements provided in the optical system compared with a case in which the chromatic aberration is not compensated and to obtain an optical element for compensating chromatic aberration used for this optical system. CONSTITUTION:A light beam emitted from a semiconductor laser 10 is converged on an optical disk 50 by means of an objective lens 40 and the reflected light by the optical disk 50 is separated from the optical path of the incident light beam by means of a beam splitter 30. In the optical system of the optical information recording/reproducing device, the beam splitter 30 is composed of two prisms 31, 32 joined together by a beam splitting surface 30a and a plano-concave lens 33 stuck to the prism 32 on the side of the objective lens 40 and the effect for generating chromatic aberration is given to the stuck surface of the prism 32 and the lens 33.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of an optical information recording / reproducing apparatus for recording / reproducing information on / from a medium such as an optical disk,
Also, the present invention relates to a chromatic aberration correction element provided in this optical system.

[0002]

2. Description of the Related Art In recent years, objective lenses for optical disks have been
A single lens with aspherical surfaces on both sides has been used for weight reduction. However, chromatic aberration cannot be corrected with an aspherical single lens.

On the other hand, a semiconductor laser used as a light source of an optical disk device shifts an emission wavelength due to a change in output power or a change in temperature. Therefore, when chromatic aberration of a lens such as an objective lens is not corrected, ,
The condensing position of the light flux may change due to the wavelength shift, which may cause an error in reading and writing information.

In order to solve this problem, the present inventors have
The present invention invented a chromatic aberration correction element in which two or three glass lenses are bonded together (Japanese Patent Laid-Open No. 3-155514 and Japanese Patent Laid-Open No. 3-1555).
55515). By using this chromatic aberration correction element in combination with an aspherical single lens, it was possible to provide a lens that is not affected by wavelength fluctuations with a smaller number of lenses than the conventional chromatic aberration-corrected lens.

[0005]

However, in the case of the means disclosed in the above publication, it is necessary to provide an element that is not directly involved in the converging action which the objective lens should originally have in order to correct chromatic aberration. Therefore, the optical system in which the chromatic aberration is corrected has a problem that both the weight and the number of parts are increased as compared with the optical system in which the chromatic aberration is not corrected.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, without increasing the number of optical elements provided in the optical system as compared with the case where chromatic aberration is not corrected. It is an object of the present invention to provide an optical system of an optical information recording / reproducing apparatus in which chromatic aberration is satisfactorily corrected, and to provide a chromatic aberration correcting optical element used in this optical system.

[0007]

In order to achieve the above-mentioned object, an optical system of an optical information recording / reproducing apparatus according to the present invention converges a light beam emitted from a light source onto an optical recording medium by an objective lens. In the optical system light of the optical information recording / reproducing apparatus that separates the light reflected by the beam splitter from the optical path of the incident light beam, the beam splitter,
Alternatively, one of the optical path deflecting elements provided between the objective lens and the beam splitter is provided with a surface for producing chromatic aberration that cancels at least the chromatic aberration produced by the objective lens.

[0008]

Embodiments of the optical system and the chromatic aberration correction element of the optical information recording / reproducing apparatus according to the present invention will be described below.

[0009]

Example 1 FIG. 1 shows an optical system of an optical information recording / reproducing apparatus of Example 1. The divergent light emitted from the semiconductor laser 10, which is the light source, is collimated by the collimator lens 20 and transmitted through the beam splitter 30.
Is converged on the optical disc 50 by. Optical disc 50
The reflected light from is incident on the beam splitter 30 again, a part of which is reflected and condensed on the light receiving element 70 via the condenser lens 60. From the light receiving element 70,
Information recorded on the optical disk or signals such as tracking error and focusing error are output in accordance with the received reflected light.

The beam splitter 30 has a light beam separating surface 3
It is composed of two prisms 31 and 32 joined by 0a and a concave plano lens 33 attached to the prism 32 on the objective lens 40 side. Prism 32 and lens 33
For example, as shown in Table 1, materials having substantially the same refractive index and different Abbe numbers are used. As a result, it is possible to generate at least chromatic aberration that cancels out the chromatic aberration generated in the objective lens 40 by the bonding surface having almost no power.

[0011]

[Table 1] Material name nA 'nd νd Prism 32 YGH51 1.74566 1.75500 52.33 Lens 33 TIH14 1.74475 1.76182 26.5 (Material name is a product name of OHARA CORPORATION)

A similar chromatic aberration correction effect can be obtained by forming a concave surface on the prism side and using a material with large dispersion, and using a material with small dispersion on the lens side as a plano-convex lens.

According to the above arrangement, the shape of the beam splitter 30 is changed as compared with the case where the chromatic aberration is not corrected, and the chromatic aberration is corrected without providing a new element. be able to.

In the first embodiment, one surface of the prism 32 is configured to be a convex surface, but this is used as a flat surface and a plano-convex lens and a convex plano lens are combined to form a chromatic aberration correcting element, which is formed by the beam splitter 30. It may be configured to be attached to.

FIG. 2 shows a modification of the first embodiment. In this example, the laser light emitted from the semiconductor laser 10 in parallel with the surface of the optical disc 50 and transmitted through the collimator lens 20 and the beam splitter 30 is reflected by the mirror 90 as an optical path deflecting member toward the optical disc 50 side, and the objective lens 4
It adopts a configuration that converges at 0. The beam splitter 30 shown in FIG. 2 includes prisms 31 and 32 'and a convex plano lens 33'.

[0016]

[Second Embodiment] FIG. 3 shows an optical system of an optical information recording / reproducing apparatus according to a second embodiment of the present invention. In this example, the beam splitter 30 is composed of two prisms 31 and 34 joined at a light beam splitting surface 30a.
On one of the light flux passing surfaces 34a, a plane perpendicular to the optical axis is formed stepwise so as to have a concave shape macroscopically as a concentric ring zone with respect to the optical axis.

The pitch P of the ring-shaped plane in the optical axis direction is expressed by the following equation, where n is the refractive index of the prism 34 and λ is a reference wavelength that does not change the wavefront, that is, does not cause chromatic aberration.

[0018]

## EQU1 ## P = λ / (n-1)

The stepped surface 34a functions as a diffraction grating, and allows the incident light to pass through without changing the wavefront when the incident light is equal to the reference wavelength, and the wavelength of the incident light is different from the reference wavelength. Then, a predetermined chromatic aberration can be generated to cancel the chromatic aberration generated in the objective lens 40.

[0020]

Third Embodiment FIGS. 4 and 5 show an optical system of an optical information recording / reproducing apparatus according to a third embodiment of the present invention. In this example,
A light beam emitted from the semiconductor laser 10 and transmitted through the collimator lens 20 passes through a beam splitter 80 having a beam shaping effect, is reflected by a mirror 90, and converges on an optical disc 50 via an objective lens 40.

The beam splitter 80 has a light beam separating surface 8
It is composed of two prisms 81 and 82 cemented with each other at 0a, and a convex plano lens 83 cemented with the prism 82.
The materials for these prisms and lenses are as shown in Table 2 below.

[0022]

[Table 2] Material name nA 'nd νd Prism 81 LAM54 1.74688 1.75700 47.82 Prism 82 TIH14 1.74475 1.76182 26.5 Lens 83 YGH51 1.74566 1.75500 52.33

Since the prisms 81 and 82 are made of materials having substantially the same refractive index and different dispersions, the optical path on the bonding surface 80a is less bent, and the beam shaping effect and the chromatic aberration correction effect can be achieved without enlarging the beam splitter 80. Can be demonstrated.

The light beam reflected by the optical disk 50 and then separated by the beam splitter 80 is focused on the light receiving element 70 via a condenser lens (not shown) as in the example shown in FIG.

[0025]

[Fourth Embodiment] FIG. 6 shows an optical system of an optical information recording / reproducing apparatus according to a fourth embodiment of the present invention. In this example, the optical path deflecting element 90 for deflecting the light flux emitted from the semiconductor laser 10 and transmitted through the collimator lens 20 and the beam splitter 30 to the optical disk 50 side is provided with a chromatic aberration correction effect.

The optical path deflecting element 90 is composed of two prisms 91 and 92 bonded together on a mirror surface 91a and a prism 9.
It is composed of a concave plano lens 93 attached to No. 2.
By using materials having substantially the same refractive index and different dispersions for the prism 92 and the lens 93, an effect of correcting chromatic aberration generated in the objective lens 40 can be exhibited. The chromatic aberration correction surface of the optical path changing element 90 may be provided on the objective lens side as in this embodiment, or conversely on the collimator lens side.

The light beam reflected by the optical disk 50 and then reflected by the beam splitter 30 is condensed on a light receiving element via a condenser lens (not shown).

[0028]

Fifth Embodiment FIG. 7 shows an optical system of an optical information recording / reproducing apparatus according to the fifth embodiment. In this example, concentric annular zones centered on the optical axis are formed in a stepwise manner in a macroscopically concave shape on the light transmitting surface 94a of the prism 94 provided as an optical path deflecting member. Is the objective lens 4
The effect of correcting chromatic aberration of 0 is exhibited.

The ring pitch and the like are the same as those described in the second embodiment. In FIG. 7, the bee splitter, the condenser lens, and the light receiving element provided between the collimator lens 20 and the prism 94 are not shown.

Also in the fifth embodiment, the stepped surface of the prism 94 may be provided on the objective lens side or, on the contrary, on the collimator lens side.

[0031]

As described above, according to the present invention, the chromatic aberration can be corrected without increasing the number of elements constituting the optical system by providing the beam splitter or the optical path deflecting element with the chromatic aberration generating effect. Optical system can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an optical system of an optical information recording / reproducing apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram of an optical system showing a modified example of the first embodiment.

FIG. 3 is an explanatory diagram showing an optical system of an optical information recording / reproducing apparatus according to a second embodiment.

FIG. 4 is a plan view showing an optical system of an optical information recording / reproducing apparatus according to a third embodiment.

FIG. 5 is a side view showing an optical system of an optical information recording / reproducing apparatus according to a third embodiment.

FIG. 6 is an explanatory diagram showing an optical system of an optical information recording / reproducing apparatus according to a fourth embodiment.

FIG. 7 is an explanatory diagram showing an optical system of an optical information recording / reproducing apparatus according to a fifth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Semiconductor laser 20 ... Collimating lens 30, 80 ... Beam splitter 30a, 80a ... Light beam separating surface 31, 32, 34, 81, 82, 91, 92, 94 ... Prism 33, 33 ', 83, 93 ... Lens 34a, 94a ... Luminous flux passing surface 40 ... Objective lens 50 ... Optical disc 60 ... Condenser lens 70 ... Light receiving element 90 ... Optical path deflecting element

Claims (8)

[Claims] 1. A beam splitter comprising: a light source; an objective lens that converges a light beam emitted from the light source onto an optical recording medium; and a beam splitter that separates reflected light from the optical recording medium from an optical path of an incident light beam. Is an optical system of an optical information recording / reproducing apparatus having a surface for generating chromatic aberration that cancels at least the chromatic aberration generated in the objective lens. 2. The beam splitter has two or more prisms joined by a light beam splitting surface and a lens bonded to at least one of the prisms, and a bonding surface of the prism and the lens. The optical system of the optical information recording / reproducing apparatus according to claim 1, wherein is a surface for generating the chromatic aberration. 3. The beam splitter has two or more prisms joined by a light beam separating surface, and at least one light beam passing surface of the prism has a concentric ring zone centered on the optical axis macroscopically. The optical system of the optical information recording / reproducing apparatus according to claim 1, wherein the stepped surface is formed to have a concave shape, and the stepped surface is a surface that causes the chromatic aberration. 4. A light source, an optical path deflecting element for deflecting a light beam emitted from the light source to an optical recording medium side, an objective lens for converging the deflected light beam on the optical recording medium, and a reflection from the optical recording medium. At least a beam splitter for separating light from an optical path of an incident light flux, wherein the optical path deflecting element has a surface for generating chromatic aberration that cancels at least chromatic aberration generated by the objective lens. Optical system. 5. The optical path deflecting member includes at least one prism and a lens bonded to at least one of the prisms, and a bonding surface of the prism and the lens causes the chromatic aberration. The optical system of the optical information recording / reproducing apparatus according to claim 4, wherein 6. The optical path deflecting member has at least one prism, and at least one light flux passage surface of the prism has a concentric ring zone centered on the optical axis and has a concave shape macroscopically. The optical system of the optical information recording / reproducing apparatus according to claim 4, wherein the optical information recording / reproducing apparatus is formed in a stepped shape, and the stepped surface is a surface that produces the chromatic aberration. 7. A surface having at least two prisms joined by a light beam separating surface and a lens bonded to at least one of the prisms, and a bonding surface of the prism and the lens causing chromatic aberration. Is a chromatic aberration correction element. 8. At least one prism, wherein at least one light flux passing surface of the prism is provided with a concentric annular zone centered on the optical axis in a stepwise manner so as to have a concave shape macroscopically. A chromatic aberration correcting element, wherein chromatic aberration is generated by the stepped surface.