JPS6089841A - Reflected light partial feedback light isolator - Google Patents

Abstract

PURPOSE:To attain ease of control of luminous amount returned to a light source by making a linear elliptic polarized converting phase plate whose optical axis is tilted by a required angle to a plate face freely turnable around a normal drawn on the plate face and providing a polarized light beam splitter with the light source. CONSTITUTION:The optical axis Z of the phase plate 8 is tilted by a required angle (0<theta<90 deg.) to the plate plane so as to be turned around the normal N drawn on the plate plane. In turning the phase plate 8 around the plate face normal N in this way, the angle between the polarized direction of the diffracted light and the crystal axis of the phase plate 8 is changed and the phase difference GAMMA is changed without changing the optical path at all. The polarized beam splitter 4 is provided between the linear elliptic polarized phase plate 8 and the light source is provided in this way, that is a 1/4 wavelength plate 5 as shown in the figure is replaced, by controlling the luminous amount returned to the semiconductor laser 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator, and particularly to a reflected light partial feedback optical isolator that optically reads or writes information from a recording medium such as an optical video/audio disc player. .

Conventionally, optical pickups for optical video disk players, etc., use a semiconductor laser 1 as a light source, as shown in FIG. The polarized light beam 9 is converted into linearly polarized light via the splitter 4, and this is converted into linearly polarized light by the quarter-wave plate 5.
After making the entire beam into circularly polarized light, it is irradiated onto bits engraved on the surface of the disk, which is a recording medium, and the reflected light is again passed through the 1/4 wavelength plate 5 to become linearly polarized light and guided to the polarized beam splitter 4. Taking advantage of the fact that the planes of polarization of the incident light and the reflected reflected light on the two surfaces of the polarizing film of the splitter 4 are orthogonal to each other, all of the reflected reflected light is reflected without returning to the light source, and is sent to the photo sensor 7. The idea was to demodulate the reflected light detected by the bit and modulated by the shape of the bit.

In an optical pickup having such a configuration, when a portion of the feedback reflected light from the recording medium passes through the beam splitter 4 and returns to the semiconductor laser 1, which is the light source, so-called backtalk is generated and demodulated. It was necessary to minimize the amount of light returning to the light source since it would impair the quality of images and sounds.

However, due to problems such as variations in the oscillation wavelength of the semiconductor laser l serving as the light source and difficulties in designing the polarizing film 2 due to this, birefringence of the protective material for the recording medium, and processing and assembly accuracy of the quarter-wave plate, etc. It has been virtually impossible to suppress the generation of light returning to the light source.

In order to solve this problem, a reflected light partial feedback type optical pickup has been proposed in which a certain amount of return light is actively given to the source 1 to reduce noise. It has been difficult to optimally control the return light t due to wavelength variations and the like.

The present invention has been made in order to solve the difficulty in optimally controlling the amount of returned light in the above-mentioned reflected light partial feedback type optical pickup. The purpose of the present invention is to provide a reflected light partial feedback optical isolator in which a polarizing beam splitter is arranged between a plate and a light source, and the phase plate can be rotated about the normal line erected directly to the plate. shall be.

Hereinafter, the present invention will be explained in detail based on its theory and embodiments shown in the drawings.

First, to help understand the present invention, the return source of the polarizing beam splitter will be briefly explained with reference to FIG.

In the same figure, when the light that has passed through the polarizing film 2 and has become a predetermined linearly polarized state enters the phase plate 8, it becomes extraordinary rays e with β and r whose refraction angles are slightly different from the incident angle α. Ordinary ray 0
Separate into two parts.

If the phase difference given by these two light rays e and 00 wavefronts when they exit the phase plate 8 is the phase difference, and if the transmittances of p-polarized light and s-polarized light of the polarizing film are tp and is, respectively, then the polarizing film 2 of the reflected light The amount of transmitted light/QT is: QT=(tpsir+4')2+tp*tsco
s"?' Give it a try.

Considering the above equation, once the design of the optical isolator is decided, tp and ts are constants that are uniquely determined by the material and structure of the polarizing film, so the amount of returned light Qt Q can be controlled by the phase difference given by the phase plate ≠ Only.

Although it is possible to vary the phase difference given by the phase plate by changing the incident angle α of the light source, using such a method involves changing the optical path, so it is not desirable or desirable. do not have.

In order to solve this problem, the present invention uses a third phase plate.
- It is configured as shown in .

That is, the required angle θ with respect to the optical axis Z6 of the plate 8 and the plate surface.
It is made to be tilted by (0 x 0 <90 degrees) and to be able to rotate about the normal line Nt erected on the board surface and the j axis.

By doing this, as is clear from the relationship between the ray ellipsoid and the optical path shown in this figure, if the phase plate is rotated around the normal to its plate surface, the polarization direction of the refracted light and the crystal axis of the phase plate can be changed. It will be appreciated that the phase difference can be changed without changing the optical path at all.

A reflected light partial feedback optical isolator capable of controlling the amount of light returned to the semiconductor laser 1 by replacing the linear-elliptic polarization conversion phase plate 8 as described above with the quarter-wave plate 5 shown in FIG. 1. can be configured.

Similarly, the optical pickup Fi according to the present invention may be configured as shown in FIG.

That is, the polarizing film 2 is attached to the side facing the light source 1 of the linear-elliptic polarization conversion phase plate 9 whose optical axis Z is inclined at a predetermined angle with respect to the plate surface, and the polarizing film 2 is arranged so as to be inclined by a predetermined angle α with respect to the optical path. At the same time, if the beam splitter can be freely rotated around the plate surface normal N, the beam splitter using an expensive right-angle prism can be saved, which will be effective in reducing manufacturing and adjustment costs.

Since the present invention is configured and functions as described above, it is possible to adjust the amount of light returned to the light source of the reflected light partial feedback optical isolator to an optimal value without changing the optical path at all. When applied to optical video/audio disc players, etc., it is extremely easy and inexpensive to improve image quality due to variations in the oscillation wavelength or beam pattern of the semiconductor laser as a light source, as well as the birefringence of the recording medium protective material.
This is extremely effective in compensating for deterioration in sound quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the general structure of a conventional optical pickup, FIG. 2 is a diagram explaining the factors of the amount of light returned to the light source, and FIG. 3 is a diagram explaining the structure of the phase plate used in the isolator of the present invention.
FIG. 8g4 is a configuration diagram showing an embodiment of an optical pickup using an optical isolator according to the present invention. Z: Optical axis, 1: Light source, 2: Polarizing film, 4:...
- Polarization beam splitter, 8... Linear-elliptical polarization conversion phase plate. N・・・・・・Normal line

Claims (1)

[Claims] (1) Linear elliptically polarized light whose optical axis is inclined at a required angle with respect to the plate surface □ Conversion A polarizing beam splitter is placed between the phase plate and the light source, and the phase plate is centered on the normal line to the plate surface. A reflected light partial feedback type □ optical isolator, characterized in that the amount of light returned to the light source is adjusted to a desired value by being rotatable. A patent characterized in that the phase plate and the polarizing beam splitter are integrated by attaching a polarizing film to the side of the phase plate facing the light source and arranging the polarizing film at a required angle with respect to the optical path. The reflected light partial feedback optical isolator according to claim 1.