JPH0261009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator used in an optical information processing device that optically reproduces recorded information stored on a recording medium such as a magnetic disk, and in particular,
The present invention relates to a technique for fixing and adjusting a quarter-wave plate of an optical isolator used in optical information processing devices incorporating a semiconductor laser into an optical system.

1 and 2 are configuration diagrams showing an optical isolator of a conventional optical information processing device. The optical isolator is a polarizing beam splitter 1 or a polarizing plate 2.
and a quarter wavelength plate 3 in combination. With this configuration, the light output from the laser diode 4 is collimated by the collimating lens 5, and then converted into linearly polarized light by the polarizing beam splitter 1 or the polarizing plate 2, and then sent to the quarter-wave plate 3.
The light is incident on the 1/4 wavelength plate, becomes circularly polarized light, and is guided to the subsequent optical system. The reflected light from the subsequent optical system passes through the 1/4 wavelength plate 3 and becomes linearly polarized light that is polarized at right angles to the previous case, so its progress is blocked by the polarizing beam splitter 1 or the polarizing plate 2. Therefore, the light does not return to the laser diode 4, which is the light source.

However, as is well known, the laser diode 4 has the property that its emission wavelength changes depending on the temperature. When the wavelength of light changes, the matching between the 1/4 wavelength plate 3 and the wavelength breaks down, so the 1/4 wavelength plate 3
The light after passing through the laser diode 4 does not become circularly polarized light but becomes elliptically polarized light, and the function as an optical isolator becomes insufficient, resulting in reflected feedback light being incident on the laser diode 4. When reflected light enters the laser diode 4, the laser diode 4 becomes unstable.
This results in a decrease in the S/N ratio, and the performance of the optical device is greatly degraded.

In view of the above problems, the present invention provides a new and useful optical isolator that prevents reflected feedback light caused by temperature changes from entering the light source by making full use of technical means to fix the quarter-wave plate. The purpose is to

Hereinafter, the present invention will be described in detail according to embodiments with reference to the drawings.

FIG. 3 is a block diagram of an optical isolator which is an embodiment of the present invention.

The polarizing plate 2 and the 1/4 wavelength plate 3 constitute an optical isolator, and the 1/4 wavelength plate 3 is held at an angle, and rod-shaped holders 6 are attached to the holding parts at both ends, and one end of the holder 6 is attached. is fixed at fixed point 7 as a cantilever beam. When the temperature rises, the expansion of the holder 6 causes the 1/4 wavelength plate 3 to tilt further, and when the temperature falls, the holder 6 shortens, causing the 1/4 wavelength plate 3 to be moved to an upright position. Therefore, even if the oscillation wavelength of the laser diode 4 disposed in the light source changes due to temperature changes, the quarter-wave plate 3
is tilted in response to this temperature change, so an optical isolator that always matches the wavelength well is constructed.

The amount of wavelength change due to the temperature of the light source has different values depending on the type of semiconductor laser, but the adjustment mechanism includes the thickness of the quarter-wave plate 3, the direction of the optical axis, the material of the holder 6, and the distance from the fixed point 7. There are many parameters such as the length and the inclination angle of the quarter-wave plate 3 when initially set, and by appropriately setting these parameters, it is possible to construct an optical isolator that always has sufficient functionality. Furthermore, this structure is extremely simple, and it becomes a very effective technique when used as an optical system for a video disk, coupled with an optical fiber that requires a wide operating temperature range and a high S/N ratio.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing the structure of a conventional optical isolator. FIG. 3 is a configuration diagram of an optical isolator showing an embodiment of the present invention. 2... Polarizing plate, 3... 1/4 wavelength plate, 4... Laser diode, 5... Collimating lens, 6... Holder,
7...Fixed point.

Claims (1)

[Scope of Claims] 1. An optical isolator using a semiconductor laser as a light source, comprising a polarizing element for linearly polarizing the output light of the semiconductor laser, and circularly polarizing the light polarized by the polarizing element. In an optical isolator comprising a quarter-wave plate for holding the quarter-wave plate, the quarter-wave plate is held by connecting both ends of the quarter-wave plate to respective ends of a thermally expanding and contracting holder; A holding angle control mechanism is provided that rotates the quarter-wave plate in accordance with thermal expansion and contraction of the holder by fixing the other end of the holder and making the direction of thermal expansion and contraction of the holder opposite. An optical isolator featuring: