JPS63187427A - Optical pickup - Google Patents

Abstract

PURPOSE:To prevent optical noise of a laser light radiated from a laser light source by providing a reflecting mirror in an optical path between the laser light source and an objective lens and forming a reflecting film causing a phase difference of nearly 1/4 wavelength to a luminous flux reflected in the reflecting mirror to the reflecting face of the reflecting mirror. CONSTITUTION:The luminous flux 11 is a nearly linearly polarized light, its polarized direction is a direction in parallel with the adhering face of the semiconductor laser 1 and the position of the luminous flux 11 around the optical axis is arranged in a direction that the polarized direction of the luminous flux 13 incident in the reflecting mirror 4 is crossed with the Z and Y axes at nearly 45 deg.. The reflecting film 4a reflects the luminous flux 13 efficiently and is constituted with a thin film made of a dielectric or the like so as to cause a phase difference of nearly 1/4 of the wavelength of the laser light with respect to the reflected luminous flux 14, then the luminous flux 14 is a circularly polarized light shown in the arrow B. The reflected light 15 from an optical disk 6 is a circularly polarized light in a direction opposite to the arrow B and the luminous flux 16 reflected in the reflecting mirror 4 is a nearly linearly polarized light shown in the arrow D nearly orthogonal to the arrow A. Since the polarized directions of the luminous fluxes 11, 18 are nearly orthogonal to each other, the optical noise of the laser beam is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for reproducing signals recorded on an optical disk, and particularly relates to an optical pickup suitable for reducing noise generated by a laser light source. .

[Conventional technology]

As a method for reducing the optical noise of the laser light emitted by the laser light source in conventional optical pickups,
As disclosed in Japanese Patent Application No. 2606, a quarter changer plate is provided in the optical path between the laser light source and the objective lens, and the polarization direction of the reflected light from the optical disk is changed to the polarization direction of the laser light emitted by the laser light source. A method of making the direction orthogonal is known.

[The gap that the invention attempts to solve]

The quarter-wave plate used in the above conventional technology is made by cutting a flat plate from an artificial quartz crystal at a precise angle to the crystal axis.
Moreover, since it is necessary to precisely control the thickness of the flat plate, there is a problem that it is extremely expensive.

An object of the present invention is to provide an optical pickup that uses an inexpensive optical element to make the polarization direction of reflected light from an optical disk perpendicular to the polarization direction of laser light emitted from a laser light source, thereby preventing optical noise in the laser light. There is a particular thing.

[Means for solving problems]

Is the purpose of the above a reflection mirror in the path between the laser light source and the objective lens? was set up and reflected by a reflective mirror.

This is achieved by forming a reflective film on the reflective surface of the reflective mirror that generates a phase difference of approximately 1/4 wavelength in the light beam.

[Effect]

Since the above-mentioned reflecting mirror performs the same function as a quarter-wave plate, it can prevent optical noise in the laser light emitted by the laser light source.

〔Example〕

The details of the present invention will be explained below with reference to embodiments shown in the drawings. FIG. 1 shows a first embodiment of an optical pickup according to the present invention, and FIG. 2 shows a part of the original pickup shown in FIG. Luminous flux 1 emitted from a semiconductor laser 1 that is a laser light source
1 enters the half mirror 2. A light semi-transmissive film 2α is formed on one side of the half mirror, and a part of the light flux 12 of the light flux 11 passes through the half mirror, but the remaining part of the light flux 13 is reflected by the half mirror and is transmitted by the collimator lens 3. The light is converted into a substantially parallel light beam and reflected by a reflective film 4α formed on the reflective surface of the reflective mirror 4. The light beam 14 reflected by the reflection mirror 4 is focused onto the optical disk 6 by the objective lens 5. The reflected light from the optical disk 6 is converted by the objective lens 5 into a substantially parallel light beam 15, reflected by the reflective film 4α of the reflective mirror 4, and incident on the collimator lens 3. The light beam 16 that has passed through the frimeter lens 6 enters the half mirror 2. A part of the light beam 18 is reflected by the half mirror and returns to the semiconductor laser 1, but the remaining part of the light beam 17 passes through the half mirror 2. and enters the photodetector 7. Information signals, focus error signals, tracking error signals, etc. recorded on the optical disc B can be detected from the output signal of the photodetector 7, but detailed explanations thereof will be omitted since they are not related to the essence of the present invention. Next, a method for reducing optical noise in the light beam 11 emitted from the semiconductor laser 1 will be explained. The light beam 11 is substantially linearly polarized light, and its polarization direction is parallel to the bonded surface of the semiconductor laser 1.

The position of the light beam 11 of the semiconductor laser around the optical axis is in the direction in which the polarization direction of the light beam 13 incident on the reflection mirror 4 intersects at approximately 45 degrees with the Z-axis and the Y-axis, as shown by arrow A in FIG. It is arranged so that. Here, the reflective film 4α efficiently reflects the light beam 13, and also reflects the reflected light beam 14.
For example, it is made of a thin film such as a dielectric material so as to generate a phase difference of approximately 1/4 of the wavelength of the laser beam. Therefore, the light beam 14 becomes circularly polarized light as indicated by arrow B.

Reflected light 15 from the optical disc 6 becomes circularly polarized light in the opposite direction to arrow B, as shown by arrow C, and light beam 16 reflected by reflection mirror 4 becomes substantially linearly polarized light, as shown by arrow A, which is substantially perpendicular to arrow A. . As a result, the polarization directions of the light beam 11 and the light beam 18 are substantially orthogonal, and optical noise in the laser beam can be prevented. In this embodiment, the reflecting mirror 4
The polarization direction of the light beam 16 incident on is the Z axis, Y4qll!
Although the direction of the arrow A intersects at approximately 45 degrees with respect to the optical disk 6, the direction of the arrow A may be used instead.In this case, the polarization direction of the light beam 16 of the reflected light from the optical disk 6 will be in the direction of the arrow A.

Further, the polarization direction of the light beam 13 may be parallel or perpendicular to the Y axis, or may be at any angle. In this case, nine reflecting mirrors 4 generate a phase difference of approximately 1/4 wavelength corresponding to the polarization direction of the light beam 16.

In addition, a reflective film 4α2 is formed so that the light beam 14 becomes circularly polarized light.

do.

FIG. 3 shows the second original pickup according to the present invention.

This is an example, and the same parts as in the first p4 are given the same numbers. FIG. 3 differs from FIG. 1 only in the reflection mirror 8. The reflective film 8α of the reflective mirror 8 reflects the luminous flux 1 of the incident light.
Corresponding to the polarization direction of 3, the reflected light beam 14 has a quarter t.
A phase difference of JI length is generated so that the light beams 14 have the same polarization.

FIG. 4 shows a third embodiment of the original pickup according to the present invention, in which the same parts as in FIG. 1 are given the same numbers. In Figure 4, the function of the reflecting mirror that generates a phase difference of 1/4 wavelength for the reflected light is shown in the half mirror 9.
is equipped. The light semi-transmissive film 9α of the half mirror 9 generates a quarter-wave phase difference in the reflected light beam 13 in accordance with the polarization direction of the incident light beam 11, so that the light beam 13?
! - configured to circularly polarize light; As a result, the polarization directions of the light beam 11 and the light beam 18 are orthogonal, and optical noise in the laser beam can be prevented.

〔Effect of the invention〕

According to the present invention, a reflective mirror is provided in the optical path between the laser light source and the objective lens, and a reflective film that generates a phase difference of approximately 1/4 wavelength in the light beam reflected by the reflective mirror is formed on the reflective surface of the reflective mirror. Therefore, optical noise in the laser beam can be prevented without using an expensive quarter-wave plate.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the optical pickup according to the present invention, FIG. 2 shows a part of the optical pickup shown in FIG. 1, and FIGS. 3 and 4 show second embodiments of the optical pickup according to the invention. Third example. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2.9... Half mirror-1 4, 8... Reflection mirror, 5... Objective lens, 6... Optical disk, 7... Photodetector. 1st country

Claims (1)

[Claims] 1. In an optical pickup equipped with a laser light source, an objective lens for focusing the laser light emitted by the laser light source onto an optical disk, and a photodetector for detecting the reflected light flux from the optical disk, the laser light source and the objective An optical pickup characterized in that a reflective mirror is provided in an optical path with a lens, and a reflective film is formed on the reflective surface of the reflective mirror to generate a phase difference of approximately 1/4 wavelength in the light beam reflected by the reflective mirror.