JPH0732287B2 - Semiconductor laser device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used for recording / erasing an optical disk memory, medical equipment and the like.

2. Description of the Related Art High-power semiconductor lasers with an optical output of 30 to 40 mW or more are elements required for recording / erasing in optical disk memories, and the demand for them is increasing more and more in recent years.

The factor that determines the maximum light output of the semiconductor laser is the light density at the end face of the laser resonator. In a semiconductor laser made of a GaAlAs crystal, when the light density at the end face exceeds 10 ⁶ W / cm ² , the crystal melts due to heat and the end face is destroyed. As a method of lowering the light density on the end face, there are a method of increasing the light emitting area on the end face and a method of lowering the end face reflectance.

A semiconductor laser is generally manufactured by cleaving a resonator, and the end face reflectance is about 30%. Normally, the laser light from one end face is used, and the laser light from the other end face is often received by the light receiving element to obtain the monitor output, so the reflectivity of the end face (rear end face) from which the monitor light is obtained is high. However, the laser light emitted from this end face is reduced. If you lower the reflectance of the end face (front end face) that takes out the laser light to the outside,
The threshold of laser oscillation increases, but the differential efficiency increases. As a result, the operating current can be reduced at high power. FIG. 4 shows the calculation result of the front facet reflectance that minimizes the operating current. It can be seen that the higher the light output, the lower the front reflectance needs to be.

As a method of lowering the end face reflectance, a thin film is generally attached to the end face. When was deposited an Al ₂ O ₃ film on the GaAs crystal, the thickness of the Al ₂ O ₃ is 0.25 wavelength (the refractive index was 1.65, the wavelength is to 8000Å 1212Å) reflectance at the minimum (about 2% ).

Problems to be Solved by the Invention However, with the above-described configuration, the reflectance cannot be sufficiently reduced, and thus a high light output cannot be obtained.

In view of the above-mentioned drawbacks, the present invention provides a semiconductor laser device coated with an end face coating film having extremely low reflectance.

Means for Solving the ProblemsThe present invention first deposits an Al ₂ O ₃ film with a film thickness of 0.15 wavelength on the end face, and then deposits a Si film with a film thickness of 0.035 to 0.050 wavelength on it. Alternatively, an Al ₂ O ₃ film is deposited to a thickness of 0.35 wavelength, and a Si film having a thickness of 0.45 to 0.47 wavelength is deposited thereon.

By thus attaching the two-layer film to the end face, the end face reflectance can be reduced to 2% or less.

Examples Examples of the present invention will be described below. FIG. 1 is an external view of a semiconductor laser device having an end face coating film according to the present invention. Since the laser light from the rear end face is usually used only for receiving a monitor output by receiving with a photodiode, four layers of Al ₂ O ₃ 1 and Si _{2 having} a film thickness of 0.25 wavelength are alternately deposited on this end face, The end face reflectance is raised to about 92%. On the front end
Al ₂ O ₃ with a thickness of 0.15 wavelength and Si 4 with a thickness of 0.04 wavelength are deposited.

FIG. 2 shows the change in reflectance when Si is deposited on the Al ₂ O ₃ films of 0.15 and 0.35 wavelengths.

When Al ₂ O ₃ has a wavelength of 0.15, Si has a minimum reflectance at a wavelength of about 0.045, which is about 0.01%. Al ₂ O ₃ is 0.3
At 5 wavelengths, Si has a minimum reflectance at about 0.455 wavelength. In the actual use, the former has better conditions for thinning the Si film because the Si film has some absorption.

FIG. 3 shows current-light output characteristics of the semiconductor laser device having the end face coating film of the present invention. Both rear end surfaces are Al ₂ O
_{It has} a 4-layer coating of ₃ / Si and a reflectance of 92%. The element B has a front surface coated with Al ₂ O ₃ having a film thickness of 0.25 wavelength and has a reflectance of about 2%. In the element A coated with the present invention, the operating current is smaller than that of the element B in the light output of 40 mW or more and in the light output of more than that. The reduction of the operating current and the reduction of the light density inside the crystal at the end face improve the reliability of the semiconductor laser device at high output.

As described above, by using the end face coating film according to the present invention, a high-power semiconductor laser device can be obtained and the reliability is also improved.
Has a great effect.

[Brief description of drawings]

FIG. 1 is an external view of a semiconductor laser device of the present invention, and FIG. 2 is
FIG. 3 is a diagram showing the reflectance with respect to the film thickness of the Si film, FIG. 3 is a diagram showing the current-light output characteristics, and FIG. 4 is a diagram showing the calculation results of the end face reflectance that minimizes the operating current. 1,3 …… Al ₂ O ₃ film, 2,4 …… Si film.

Claims (1)

[Claims] 1. An Al ₂ O ₃ film having a thickness corresponding to 0.15 wavelength on at least one of the cavity end faces, and 0.035 to 0.
Has a Si film with a thickness equivalent to 050 wavelengths, or
A semiconductor laser device comprising an Al ₂ O ₃ film having a thickness corresponding to 0.35 wavelength and a Si film having a thickness corresponding to 0.45 to 0.47 wavelength formed thereon.