JPH01166586A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To reduce returning light to the inside of a semiconductor laser and noises caused thereby by applying a reflection coating of a specified reflection factor to the front of a laser and a reflection coating of a reflection factor higher than that of the front to the rear. CONSTITUTION:Coating of two layers and four layer of SiO2, amorphous Si is applied to the front of a laser chip 1 of pulsation semiconductor laser as a front reflection film 2, controlling the reflection factor to be 40-70%. Similarly, coating of SiO2, amorphous Si four layer is applied to the rear of the chip 1 to form a rear reflection film 3 making the reflection factor of 90% higher than the front reflection factor. In this way, returning light into the chip 1 and noises caused thereby are reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to semiconductor lasers.

[Conventional technology]

Conventionally, when using a semiconductor laser as a light source for reading information, the following four cases have been used for the reflectance of the laser end face.

l) ~30% reflectance on both sides.

2) ~10% reflectance on the front surface and ~100% reflectance on the entire rear surface.

3) 270% reflectance on both sides.

4) Reflectance of ~10% on the front side and ~30-30 on the back side.

3) Increasing the reflectance of both end faces has not been attempted for anything other than longitudinal single mode lasers.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the end face treatment for further reducing the noise of the pulsation semiconductor laser, and there is a problem that large noise is generated when the number of lights returned to the laser is several inches or more. there were.

An object of the present invention is to provide a pulsation semiconductor laser with lower noise.

[Means for solving problems]

The pulsation semiconductor laser has relatively no increase in noise relative to the return source. However, if there is a large amount of returned light exceeding 0.5%, large noise will occur. In order to reduce this noise, the amount of light returning into the semiconductor laser can be reduced by increasing the reflectance of the laser end face.

[Effect]

A reflective coating on the front side reduces light returning from outside the laser, reducing noise. At this time, to increase the efficiency of light extraction to the front.

It is necessary to apply a coating with higher reflectivity to the rear surface than to the front surface. To simply reduce noise.

The higher the reflectance of the front surface, the greater the effect. However, when the reflectance of the front surface is set to 70% or more, pulsation does not occur. Therefore, the reflectance of the front surface needs to be 70% or less.

〔Example〕

An embodiment of the present invention will be explained with reference to FIG. In front of the semiconductor laser l (semiconductor laser chip part shown)
z, two-layer and four-layer coatings of amorphous Si were used to control the reflectance between 40 and 90%. The rear part 3 was similarly coated with four layers of S 10 ze amorphous Si to give a reflectance of 9096. Using this element, we drove a semiconductor laser with an output of 2 to 6 mW, which is normally used when reading optical discs, etc., and found the worst value of noise under the condition of 5 inches of returned light. FIG. 2 shows the relationship between the worst value of noise and the forward reflectance. The reflectance without reflective coating is ~32%, and by using reflective coating and increasing the forward reflectance t to 40% or more, the noise can be reduced to 5 dB.
It is possible to reduce the amount by more than 100%. On the other hand, FIG. 3 shows the percentage of elements that produce pulsation in the output range of 2 to 6 mW when the forward reflectance is varied. At reflectance of 70% or more,
The probability of producing a pulsation decreases rapidly. Elements that do not produce pulsation oscillate in a single longitudinal mode,
The noise will be 10-"H2 or more. Considering the above points, it is not practical to increase the forward reflectance to 70% or more. On the other hand, if the forward reflectance is set to 40 to 80%, the pulsation will be reduced. The resulting rate decrease is small and the noise t-5dB
It is possible to reduce the amount by more than 100%. In this embodiment, the rear reflectance is 90%, which is greater than the front reflectance. This is because if only the front side has a high reflectance, the amount of light emitted to the rear will be large and the output efficiency will deteriorate, so by increasing the reflectance at the rear compared to the front, it is possible to suppress the deterioration in output efficiency. There is. In this example, the rear reflectance t-90
%, but this should be higher than the forward reflectance from the above point.

〔Effect of the invention〕

According to the present invention, the noise of a pulsation semiconductor laser can be improved by 5 to 20 dB.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a semiconductor laser. FIG. 2 is a diagram showing the relationship between forward reflectance and laser noise. FIG. 3 is a diagram showing the relationship between the forward reflectance and the proportion (probability) of elements that cause pulsation. Yahegeta・Vinegar 9

Claims (1)

[Claims] 1. In a pulsation semiconductor laser that generates pulses when operated with direct current, there are 40 to 70
1. A semiconductor laser device characterized by having a reflective coating on the rear surface with a reflectance of 1.5% and a reflective coating on the rear surface with a higher reflectance than the front surface.