JPS61126644A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain an inexpensive small-sized optical pickup using no polarizing beam splitters by using a diffraction grating which consists of a material having circular dichroism and has the laser light dividing function. CONSTITUTION:The light having about 0.8mum wavelength emitted from a semi conductor laser 1 is converted to parallel light by a collimator lens 2 and is converted to a clockwise circularly polarized light by a 1/4 wavelength plate 5 and is divided to three beams (omitted in the figure) of 0th order and + or -1st orders, and they are made incident on a cholestric polymer film 11. Since the film 11 has the transmission property of the clockwise circularly polarized light, three divided beams are transmitted through the film 11 and are converged by a condenser lens 6 and are focused on a disc 7 as three spots. The reflected light from the disc 7 is a counterclockwise circularly polarized light and is restored to parallel light by the condenser lens 6 and is reflected on a slope 13 of the film 11 and passes a light receiving lens 8 and a cylindrical lens 9 and is made incident on a photodiode 10. Thus, a diffraction grating consisting of an organic matter having the circular dichroism is used to simplify the struc ture of the optical pickup.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical pickup that writes or reads information using coherent light.

(Conventional structure and its problems) An optical pickup focuses coherent light emitted by a laser to write information on an information recording medium such as a disk, or reads recorded information.The main part of the optical pickup is an optical pickup. It consists of a system and a drive system.

An optical pickup using a conventional semiconductor laser will be explained with reference to FIG. In the figure, light with a wavelength of 0.8 μm emitted by a semiconductor laser 1 is turned into parallel light by a collimator lens 2, split into 3 beams by a diffraction grating 3 (not shown), and then divided into 3 beams by a polarizing beam splitter 4 and a quarter-wavelength beam. After being converted into circularly polarized light by the plate 5, the reflected light from the disk 7 is converged by the condenser lens 6 and connects three spots with a diameter of approximately 1 μm on the disk 7.
The light returns to parallel light, is converted into linearly polarized light orthogonal to the incident light by the quarter-wave plate 5, is reflected by the polarizing beam splitter 4, changes its direction by 90'', is converged by the light receiving lens 8, and then is reflected by the cylindrical lens. 9 and enters the photodiode 10, which converts it into an electrical signal.At this time, the divided three beams detect the deviation in the radial direction of the disk 7, and the cylindrical lens 9 detects the deviation of the focal point. The optical system is finely adjusted and corrected to the correct position by the system 11. However, the polarizing beam splitter 4 is an essential component in an optical pickup with such a configuration, and therefore, there is a problem that it is large and extremely expensive. In addition, it is difficult to mass-produce the polarizing beam splitter 4, and the mass production of other parts is getting on track1. For example, when it comes to lenses, it is now possible to mass-produce them by using plastic. This was a problem with mass production.

(Object of the Invention) The present invention aims to eliminate the above-mentioned drawbacks, and provides an inexpensive, compact optical pickup that does not use a polarizing beam splitter.

(Structure of the Invention) In order to achieve the above object, a diffraction grating made of a material having circular dichroism and having a laser beam splitting function is replaced with a polarizing beam splitter and a diffraction grating to reduce the number of component parts. This is an attempt to obtain a small, inexpensive optical pickup.

(Explanation of Examples) An embodiment according to the present invention will be explained with reference to FIG.

This figure is a configuration diagram of an optical pickup according to the present invention, and shows the structure of the optical pickup according to the present invention.
A cholesteric polymer film 11 made of γ-butyl-L-glutamate) and triethylene glycol methafrylate on which a diffraction grating 12 was formed was used.

The cholesteric polymer film 11 is an organic material having circular dichroism, and has the property of transmitting right-handed circularly polarized light but reflecting left-handed circularly polarized light.

On the lower surface of this cholesteric polymer film 11, a replica is taken by photopolymerization to form a diffraction grating 12.
An inclined surface 13 for changing the traveling direction of light is provided on the upper surface.

Light with a wavelength of 0.8 μm emitted by the semiconductor laser 1 is turned into parallel light by the collimator lens 2, converted into right-handed circularly polarized light by the quarter-wave plate 5, and then converted into 0th-order light and ±1st-order light by the diffraction grating 12. The beam is divided into three beams (not shown) and enters the cholesteric polymer film 11. Since the cholesteric polymer film 11 has right-handed circularly polarized light transmittance, the three divided lights are transmitted and converged by the condenser lens 6 to form three spots on the disk 7. The reflected light from the disk 7 becomes left-handed circularly polarized light and returns to parallel light at the condenser lens 6, and then is reflected by the inclined surface 13 of the cholesteric polymer film 11 and enters the photodiode 10, which passes through the light receiving lens 8 and the cylindrical lens 9. . Note that the drive system is the same as the conventional example.

Note that in the above embodiment, the cholesteric polymer film 11 was used, but the material is not limited to this as long as it is an organic substance having circular dichroism. Further, the structure of the optical pickup is not limited to the structure mentioned in the embodiment, but may be any structure using a diffraction grating made of an organic substance having circularly polarized light dichroism.

In this way, the structure can be simplified by using a diffraction grating made of an organic substance having circular dichroism.

(Effects of the Invention) As explained above, according to the present invention, there is no need to use a polarizing beam splitter that is not only large in size but also difficult to mass-produce, and a compact optical pickup that can be mass-produced and is inexpensive can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional optical pickup, and FIG. 2 is a block diagram of an optical pickup according to the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Collimator lens, 3.12... Diffraction grating, 4... Polarizing beam splitter, 5... Quarter wavelength plate, 6... Condensing lens, 7... Disc, 8... Light receiving lens,
9... Cylindrical lens, 10... Photodiode,
11...Cholesteric polymer film, 13
...Slope surface. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2

Claims (2)

[Claims] (1) An optical pickup characterized by using a diffraction grating made of a material having circular dichroism and having a laser beam splitting function. (2) The optical pickup according to claim (1), characterized in that a cholesteric polymer film is used as the material having circular dichroism.