JPH05314536A - Beam splitter and optical pickup - Google Patents

Abstract

PURPOSE:To improve the space efficiency and the cost of parts and also to reduce the weight of the optical system of an optical pickup. CONSTITUTION:The optical system of an optical pickup is constituted by a beam splitter 100 having the aspherical reflecting surfaces 101 and 103 or an aspherical spectral surface 102. Thereby, since the aspherical reflecting and spectral surfaces have the roles of a collimator lens, an objective lens, a signal detecting condenser lens, etc. Thus the expensive optical parts are not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup in a recording / reproducing apparatus using an optical recording medium such as an optical disk.

[0002]

2. Description of the Related Art Conventionally, a beam splitter, which is a spectroscopic means, and a lens, which is a condensing means, have distinct roles, and each of them is constituted by an independent optical component.

[0003]

However, since the conventional methods require independent optical components,
Space efficiency was poor and parts cost was high.

[0004]

The structure of the present invention for solving the above-mentioned problems is (1) a beam splitter having an aspherical spectral surface, and (2) a beam splitter having an aspherical reflecting surface. (3) The beam splitter and the light receiving element according to (1) above, and the light reflected from the optical recording medium is partially reflected by the spectral surface of the beam splitter and is incident on the light receiving element. That, (4)
The beam splitter and the light receiving element described in (1) above are incident, and the light beam incident on the beam splitter is partially reflected by the spectral surface of the beam splitter and condensed on the optical recording medium.
The reflected light from the optical recording medium is configured to partially penetrate the spectral surface of the beam splitter and enter the light receiving element,
(5) The beam splitter according to (2) above is configured to convert divergent light emitted from a light source into substantially parallel light through a reflecting surface, (6) the beam splitter according to (2) above. Is used to collect the light on the optical recording medium after being reflected by the reflecting surface.

[0005]

【Example】

(Embodiment 1) FIG. 1 shows an optical pickup according to an embodiment of the present invention. In the figure, 1 is a light source such as a semiconductor laser, 10 is an optical recording medium, 100 is a beam splitter relating to the present invention, and 201 is a light receiving element for signal detection which is composed of a four-division sensor. 2 shows the beam splitter 100 in FIG.
The figure seen from the A direction is shown.

The beam splitter 100 has aspherical reflecting surfaces 101 and 103 and an aspherical spectral surface 1 as well.
02 is formed. The spectral surface 102 is a joint surface of the two prisms 110 and 120, and is coated with a dielectric film. Each of the aspherical surfaces 101 and 103 is basically a parabolic surface, but some aberration correction is performed. The reflective surfaces 101 and 103 are coated with a metal such as silver or a dielectric film to ensure a reflectance close to 100%.

The divergent light beam 20 emitted from the light source 1 enters the beam splitter 100 and is reflected by the aspherical reflecting surface 101 to become a parallel light beam 21. Here, the light emitting point position of the light source 1 is placed at a position substantially close to the focus of the parabolic surface which is the basic shape of the aspherical reflecting surface 101. The parallel light beam 21 partially passes through the aspherical spectral surface 102 and is reflected again by the aspherical reflecting surface 103 to become a focused light beam 22. When the recording surface of the optical recording medium 10 is at a position substantially close to the focus of the parabolic surface which is the basic shape of the aspherical reflecting surface 103, the condensed light flux 22 forms a spot on the optical recording medium 10.

That is, the aspherical reflecting surface 101 has the same function as a collimator lens used in a conventional optical pickup, and the aspherical reflecting surface 103 is also equivalent to an objective lens used in a conventional optical pickup. It has the action of and is a characteristic content in the present invention.

Next, the reflected light modulated by the recording surface of the optical recording medium 10 retraces the above optical path and becomes a parallel light beam 21 again in the beam splitter 100. A part of the parallel light flux 21 is reflected by the aspherical spectral surface 102 and becomes a focused light flux 23. The aspherical spectral surface 102 is the reflection surface 1 described above.
Unlike 01 and 103, the reference parabolic surface is modified so that astigmatism is intentionally generated. Therefore, by arranging the light receiving element 201 at the position of the minimum confusion circle of the focused light beam 23, that is, substantially at the center of the astigmatic difference, the focus error signal, the track error signal, and the reproduction signal can be detected as in the conventional astigmatism method. ..

Therefore, it is not necessary to separately prepare expensive optical parts such as a collimator lens, an objective lens and a condensing lens for signal detection as in the prior art, and these functions are the only optical parts. It can be integrated in the splitter 100. Although not shown in the figure, the optical pickup including the beam splitter 100, the semiconductor laser 1 and the light receiving element 201 is integrated into a focus direction (direction orthogonal to the optical recording medium surface) and a track direction (optical recording medium). Driven in the radial direction of the surface). An electromagnetic actuator or the like can be used as the drive mechanism, and the drive in the track direction is arbitrary such as a parallel movement type or a type of rotating around an axis. On this occasion,
It is also a feature of the present invention that the movable mass driven by the electromagnetic actuator is light in weight because there are few optical parts.

(Embodiment 2) FIG. 3 shows an optical pickup according to another embodiment of the present invention. In the figure, 10 is an optical recording medium, 300 is a beam splitter according to the present invention, and 401.
Is a light receiving element for signal detection which is composed of a two-divided sensor.

An aspherical spectral surface 301 is formed on the beam splitter 300. The spectral surface 302 is a joint surface of the two prisms 310 and 320, and is coated with a dielectric film. The aspherical spectral surface 301 is basically a parabolic surface, but with some aberration correction.

A light beam emitted from a light source such as a semiconductor laser is converted into a substantially parallel light beam 31 by a collimator lens (not shown).
Next, it enters the beam splitter 300. Parallel light flux 3
1 is partly reflected by the aspherical spectral surface 301, and the condensed light beam 32
Becomes The recording surface of the optical recording medium 10 is an aspherical spectral surface 301.
When it is at a position that is almost close to the focus of the parabolic surface that is the basic shape of
The condensed light flux 32 forms a spot on the optical recording medium 10.

The reflected light modulated by the recording surface of the optical recording medium 10 traces the above optical path in reverse, and the beam splitter 30.
Part of the light is transmitted through the aspherical spectral surface 301 within 0, and the divergent light beam 3
It is emitted as it is to the outside of the beam splitter 300. If the light receiving element 401 is placed here, the far-field image of the reflected light can be detected, and the track error signal by the so-called push-pull method can be detected by taking the differential of the light receiving element 401 divided into two. Further, the reproduction signal is detected by taking the total sum of the two divisions of the light receiving element. The remaining light flux that is not transmitted by the aspherical spectral surface 301 is reflected to become a parallel light flux 31. A part of the parallel light flux 31 is incident on a focus error detector (not shown) and converted into a focus error signal. It should be noted that the second embodiment is not one in which all the optical components required for the optical pickup are integrated into one as in the first embodiment, but at least the objective lens can be eliminated. Further, since the reflected light from the optical recording medium 10 diverges greatly, the enlarged far field image also becomes large, and the alignment accuracy of the light receiving element 401 can be loosened.

By the way, the beam splitters 100 and 300 used in each of the above embodiments are made by joining a plurality of prisms having an aspherical surface, but it is difficult to form the aspherical surface by a polishing process. Therefore, it is efficient to perform injection molding with transparent resin or hot press molding with optical glass. These molding techniques have made remarkable progress in recent years, and nowadays a large number of aspherical lenses and prisms with extremely small optical aberrations are supplied. Therefore, it can be said that the present invention is highly practicable and has specificity.

[0016]

As described above, according to the present invention, since the optical system of the optical pickup is constituted by the beam splitter having the aspherical reflection surface or the aspherical spectral surface, the optical system for the collimator lens, the objective lens or the signal detection is used. It is no longer necessary to separately prepare expensive optical components such as the condenser lens. Therefore, with respect to the optical system of the optical pickup, the space efficiency and the component cost can be improved and the weight can be reduced, which can contribute to the spread of the optical recording / reproducing apparatus and the performance improvement.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical pickup according to a first embodiment of the invention.

FIG. 2 is a diagram showing a beam splitter according to the first embodiment of the present invention, which is a shape seen from the direction A in FIG.

FIG. 3 is a diagram showing an optical pickup according to a second embodiment of the invention.

[Explanation of symbols]

 1 light source 10 optical recording medium 100,300 beam splitter 201,401 light receiving element 101,103 aspherical reflective surface 102,301 aspherical spectral surface

Claims (6)

[Claims] 1. A beam splitter having an aspherical spectral surface. 2. A beam splitter having an aspherical reflecting surface. 3. The beam splitter and the light receiving element according to claim 1, wherein the reflected light from the optical recording medium is partially reflected by the spectral surface of the beam splitter and is incident on the light receiving element. An optical pickup featuring. 4. The beam splitter and the light receiving element according to claim 1, wherein a light beam incident on the beam splitter is partially reflected by a spectral surface of the beam splitter and condensed on an optical recording medium, An optical pickup characterized in that reflected light from an optical recording medium is configured to partially pass through a spectral surface of the beam splitter and enter the light receiving element. 5. An optical pickup using the beam splitter according to claim 2, which is configured to convert divergent light emitted from a light source into substantially parallel light via the reflecting surface. 6. An optical pickup comprising the beam splitter according to claim 2 and configured to be reflected by the reflecting surface and focused on an optical recording medium.