JPS6077480A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To reduce the emitting light from the rear end surface by alternately coating dielectric such as SiO2, Al2O3 and Si in four layers, on the ends, and setting the reflectivity of the rear end to the prescribed value. CONSTITUTION:A coating is not formed on the side for emitting forward the laser light, but the side is used while maintaining the reflectivity at 32%. Dielectric and Si are alternately coated in four layers on the rear end of the resonator of the reflecting side. The thicknesses t1-t3 of various types are set to 1/4 of the wavelength (lambda) of the laser light in the layer. The thickness t4 of the Si 5 of the final fourth layer is set to approx. 1/6 of the wavelength. When the front end light output is Pf, and the rear end light output is Pr, the light output ratio Pf/Pr can be represented as the formula I with the reflectivities Rf, Rr. Accordingly, when the rear end light output for obtaining necessary monitor pin current is decided, the reflectivity of the rear end is obtained, and the thickness can be determined. Thus, the emitting light from the rear end can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device used at the core of optical information processing devices such as optical fiber communications, optical disks, and laser solintors.

Therefore, it has come to occupy a very important position.

Incidentally, in a semiconductor laser, the resonator usually utilizes an open plane of a ■-V group compound semiconductor. In this case, for example, in GaAs, light with a wavelength near the band catch (800
The refractive index of GaAa for the wavelength range (nm ~ 850 nrri) is about 36, and the reflectance of the cavity end face is about 32%.

In conventional semiconductor lasers, both end faces of the resonator are used with the same reflectance of approximately 32%, and the same amount of laser light is emitted from the end face that does not extract light from the laser stem. Ta. This laser light is received by a pin photodiode built into the stem and used to monitor the laser light output, but the laser light reflected from the pin photodiode surface comes out to the front and causes cost. easy. In addition, in order to use it as a monitor light for obtaining the bottle current, the light output needs to be smaller than the light emitted from the front end face, so by coating the surface with a dielectric multilayer film, the bottle current can be obtained above the allowable value. The present invention provides a structure of a semiconductor laser device that suppresses light emitted from the rear end facet to a certain extent.

(Structure of the Invention) In order to achieve this object, the semiconductor laser device of the present invention is based on 5i02 r At203. The end face is coated with four layers of dielectric material such as Si3N4 and 81 alternately, increasing the reflectance of the rear facet from 32% to 70% to 90%, thereby reducing the amount of light emitted from the rear facet. .

(Description of Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a dielectric material and Si on one side of the laser tick of the present invention.
This shows how the four-layer film is coated. 1 is a semiconductor laser chip. Reference numeral 6 denotes the front end face of the resonator, which is the side from which the laser beam is extracted forward. No coating is applied to this side, and the reflectance is used as it is at 32 inches, or a dielectric material with a half wavelength film thickness that does not change the reflectance is coated. A dielectric material (S
+02 rAz2o, l813N4, etc.) and St are alternately coated in four layers. 2 and 4 are dielectrics,
3 and 5 are Si. The various film thicknesses t1%t3 are set such that the wavelength λ of the laser light in the layer is one fourth. The film thickness t4 of the fourth and final layer of Si 5 is made thinner than 1/4 wavelength, and approximately 1/6 wavelength. This is because if the wavelength is set to 1/4, the reflectance is too high and the light emitted from the rear end face is too small, making it impossible to obtain a sufficient monitor bin current. A high frequency sputtering device is used to form the dielectric and Si films. In this case, the Si film is deposited as amorphous Si.

The refractive index of each dielectric and the laser oscillation wavelength are 0.82 μm.
Table 1 shows the film thickness corresponding to 1/4 wavelength. Further, the calculation results of the reflectance of each dielectric and the four-layer film of Sl are shown in FIGS. 2 to 4. For example, when At206 is used as the dielectric material, the thickness of the fourth layer sl is changed from O to λ/
It can be seen that by changing the reflectance up to 4, the reflectance can be controlled from 47% to 93%.

Table 1: If the front end surface optical output is Po and the rear end surface optical output is Pr, the optical output ratio Pf/Pr of the front end surface and the rear end surface is determined by the respective reflectances R,
, Rr is expressed as follows.

pf/pr= (Rr/R,)1A((x −RO/(
1-Rr)) FIG. 5 shows the optical output ratio Pf/Pr when the reflectance of the front end face is set to 32 cm, which is the value when no coating is applied, and the reflectance of the rear end face is changed.

From the above, when the rear facet light output to obtain the required monitor bin current is determined, the reflectance of the rear facet increases and the 81
The film thickness can be determined. Calculated results and experimental values of the relationship between the semiconductor laser height, the threshold current process th, the chemical process th/'th, and the reflectance Rr of the rear facet before the semiconductor laser beam height, - child, sor drop, and the threshold current process th. It is shown in FIG.

(Effects of the Invention) As described above, in the present invention, by coating the rear facet of a laser with a four-layer film of dielectric and Si, the reflectance of the rear facet can be set to a desired value, and light from the rear facet can be set to a desired value. Monitor the output
It can be reduced to the value required to obtain the bin current.

As a result, there is an effect of suppressing the light reflected on the surface of the bottle photodiode from becoming a cost and emitting to the front. Further, unnecessary light is not emitted to the rear end facet, the threshold current of the laser can be lowered, and the differential quantum efficiency of the front end facet can be increased. Further, FIG. 7 shows the relationship between the ratio η'of/ηDf of the differential quantum efficiency of the front end face before and after coating and Rr.

In both cases, the front end surface is not coated. (Reflectance 3
2%). It can be seen that by setting the reflectance of the rear facet to 50% to 90%, the threshold current can be improved by 10% to 20%, and the differential quantum efficiency can be improved by 20% to 50%. As a result, the operating current of the semiconductor laser can be significantly reduced, and a tremendous effect on improving the reliability of the semiconductor laser can be expected.

[Brief explanation of drawings]

FIG. 1 shows a semiconductor laser chip showing an embodiment of the present invention, and FIGS. 2, 3, and 4 show a dielectric and St.
Figure 5 is a diagram showing the calculation results of the reflectance when four layers are coated alternately. Figure 5 is a diagram showing the calculation results of the reflectance Rr of the rear end face and the optical output ratio Pf/Pr of the front end face and the rear end face. The figure shows the division results and experimental values of the threshold current ratio 1h/'th before and after changing the reflectance of the rear facet, and Figure 7 also shows the ratio η of the differential quantum efficiency, /
η. A diagram showing the calculation results and experimental values of . 1... Semiconductor laser chip, 2, 4... Dielectric film,
3...Amorphous Si film, 5...Amorphous S
i-film, 6... front end surface of semiconductor radar. Figure 1 Figure 2 R (%) Figure 3 R (%) Figure 4 R (%) Figure 6 7th / Ith Rr (Rf = Rr (Rf- 0,32) 0.32)

Claims (1)

[Scope of Claims] (Re: A semiconductor laser device in which one of the resonator end faces is covered with a four-layer film consisting of a dielectric layer and a Si layer on the open arm surface. (2) Of the four-layer film, one of the dielectric Alternating body layer and Si layer 3
The semiconductor laser device according to claim 1, wherein the layer is formed with a thickness corresponding to a quarter wavelength.