JPS62256488A - Semiconductor laser device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used as a light source for optical disc files, and more particularly to a semiconductor laser device suitable as a light source for recordable and reproducible optical discs.

[Conventional technology]

Conventionally, a single high-output semiconductor laser has been used as a light source for optical discs capable of recording and reproducing.
During playback, it was operated at low output.

However, as the sensitivity of recording films has increased, erroneous recording by laser light has started to occur during reproduction, and reproduction with lower optical output has become necessary. However, in order to increase the output power of conventional lasers, the laser end face has a low reflectance, which causes problems in that quantum noise is generated during low output operation, and return optical noise is easily generated. Return optical noise is discussed, for example, in Proceedings of the Japan Society of Applied Physics, Autumn 1982, 139-R-4.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a light source for an optical disk for recording and reproducing which has sufficiently low quantum noise even when operating at low optical output during reproduction, and has far less return light induced noise, and which operates at high output during recording. It is in.

[Means for solving problems]

The above object is achieved by arranging two semiconductor lasers as light sources, which can be modulated independently of each other and whose end face reflectances are significantly different from about 10% to about 90%, adjacent to each other in parallel with an interval of about 300 μm.

[Effect]

Since the emitted light from two semiconductor lasers arranged in parallel with a spacing of about 300 μm is extremely close to each other, they can be focused onto an optical disk using the same optical system, making recording and recording possible.
The same optical system can be used for playback. Also, among the two semiconductor lasers, the front end face reflectance of one laser is 5 to 1.
It is as low as 0%. Therefore, highly efficient and high power laser light is emitted from the front end face of this laser, allowing efficient recording. The other laser end face has a forward reflectance of 75~
As a result, the differential quantum efficiency of the element is low, and the quantum noise level is low even when operating at a low optical output of 0.5 to 1 mW.Also, due to the high reflectance, it is effective against return light from the disk. It's also stable.

Return light induced noise is reduced.

〔Example〕 The present invention will be explained in detail below.

[Example 1] In FIG. 1, 1 and 2 represent first and second semiconductor lasers, and 3 represents a laser mount. The front end facet of the first semiconductor laser 1 has a low reflectance film (reflectance of approximately 10%) 4 made of 5iOa film with a thickness of 1/3.5 wavelength, and the rear end facet has a film with a thickness of 1/4 wavelength. A two-layer high-reflectance film (reflectance of about 75%) 5 is formed, with one layer each of 5ift and a-3i films. On the other hand, in the case of the second semiconductor laser 2, contrary to A, a high reflectance film is formed on the front end face and a low reflectance film is formed on the rear end face. Semiconductor lasers A and B are bonded to a laser mount 3 with a chip spacing of about 50 μm, laser stripes parallel to each other, and pn junctions facing upward. The width of the laser chip is approximately 300 μm, and the distance between lasers A and B is approximately 350 μm. A
and B are wire bonded and can be driven independently of each other. As semiconductor lasers A and B, elements having a CSP structure were used.

This semiconductor laser device was mounted on an optical disk pickup, and the stripe spacing of the six lasers whose characteristics were studied was approximately 3.
Because they are extremely close to each other at 50 μm, we were able to focus the spots of both lasers on the optical disk using the same optical system.
Next, recording on the disc was performed by driving the first laser with an optical output of 30 mW. During reproduction, the second laser was operated continuously with an optical output of about 1 mW to read the signals on the disk. Since the second laser has a high reflectance of about 75% at its front end face, it was confirmed that it is extremely stable against the return light from the disk. In addition, due to the high reflectance, the quantum noise level is low, making it possible to read signals with a high S/N, and the relative noise intensity during playback is 10
A value of "Hz-" or less was obtained. Furthermore, during reproduction using the second laser, a dc lightning current of 700 to 1000 M
It has been found that the noise level during reproduction can be further reduced by using a high frequency of Hz.

[Example 2] A second embodiment of the invention will be described with reference to FIG.

In FIG. 2, the same effect as in Example 1 was obtained in a semiconductor laser device having a six-layer structure in which semiconductor lasers 1 and 2 of Example 1 were integrated seven times on the same substrate.

In Examples 1 and 2, the front and rear end face reflectances of the first and second semiconductor lasers were set to 10% and 75%.
However, it goes without saying that the effect of the present invention can be obtained by lowering the reflectance of one laser and increasing the other.In addition, in the embodiment, the reflectance of the rear end facet of the first semiconductor laser is changed to the reflectance of the second laser. Reflectance of the front facet of the semiconductor laser, second
We have described the case where the rear end face reflectance of the first laser is the same as the front reflectance of the first laser.
This is because manufacturing is easy, such as by simply mounting lasers manufactured in the same process in opposite directions.1 It goes without saying that the effects of the present invention can be obtained depending on the value of the rear end face reflectance. .

〔Effect of the invention〕

According to the present invention, it is possible to obtain a semiconductor laser which has low optical noise and is particularly suitable as a light source for optical disk files.

[Brief explanation of drawings]

FIG. 1 is a plan view of a semiconductor laser device according to a first embodiment of the present invention, and FIG. 2 is a plan view of a semiconductor laser device according to a second embodiment of the present invention. rLl! This is Figure 18. DESCRIPTION OF SYMBOLS 1...First semiconductor laser, 2...Second semiconductor laser, 3...Laser mount, 4...Low reflectance end face coating film, 5...High reflectance end face coating film . -Figure 1'''fI 2

Claims (1)

[Scope of Claims] 1. A semiconductor laser device characterized in that two semiconductor lasers having different end face reflectances and capable of mutually independent modulation are arranged adjacently in parallel. 2. A semiconductor laser device according to claim 1, wherein the two semiconductor lasers are monolithically integrated on the same substrate.