Semiconductor laser device and method of fabricating the same

Abstract

A monolithic two-wavelength semiconductor laser device includes a front end face film 19 on a resonator front end face 18, and a high-reflectivity end face film 22 as a multilayered film on a resonator rear end face 21. The front end face film 19 is formed using a low-refractive-index material, and the film thickness is so set that the reflectivity is 20%. The high-reflectivity end face film 22 is formed by alternately stacking thin films of low- and high-refractive-index materials, and the film thickness is so set that the reflectivity is 80%. The film thickness of each of these two end face films is calculated by an optical length d=(1/4+j)×λm by using a mean value λm=(λ 1+λ2 )/2 of the oscillation wavelengths of the two semiconductor laser diodes. This makes it possible to obtain an end face film having a desired reflectivity and capable of being formed at once, and to fabricate a two-wavelength semiconductor laser device having high reliability, meeting the required performance, and also having high productivity.

What is claimed is:  
     
         1 . A semiconductor laser device comprising: 
 a substrate;    a first laser element portion formed on said substrate to oscillate laser light having a first wavelength;    a second laser element portion formed on said substrate to oscillate laser light having a second wavelength;    a front end face film formed at once on front end faces of said first and second laser element portions and having a uniform film thickness; and    a rear end face film formed at once on rear end faces of said first and second laser element portions, having a uniform film thickness, and comprising a plurality of thin films,    wherein the film thickness of said front end face film and said plurality of thin films of said rear end face film have an optical length d=(1/4+j)×λ(j=0, 1, 2, . . . ) with respect to a mean wavelength λ of the first and second wavelengths.    
     
     
         2 . A device according to  claim 1 , wherein said front end face film has a reflectivity of 3 to 37%, and said rear end face film has a reflectivity of not less than-75%.  
     
     
         3 . A device according to  claim 1 , wherein said front end face film is made of a low-refractive-index material having a refractive index n<1.8, and said rear end face film comprises stacked layers of thin films made of a low-refractive-index material having a refractive index n<1.8 and thin films made of a high-refractive-index material having a refractive index n>1.9.  
     
     
         4 . A device according to  claim 1 , wherein said front end face film is made of Al 2 O 3 , and said rear end face film comprises stacked layers of thin films made of a low-refractive-index material selected from the group consisting of Al 2 O 3  and SiO 2  and thin films made of a high-refractive-index material selected from the group consisting of SiN 4  and Si.  
     
     
         5 . A device according to  claim 3 , wherein said front end face film is made of Al 2 O 3 , and said rear end face film comprises stacked layers of thin films made of a low-refractive-index material selected from the group consisting of Al 2 O 3  and SiO 2  and thin films made of a high-refractive-index material selected from the group consisting of SiN 4  and Si.  
     
     
         6 . A semiconductor laser device fabrication method comprising the steps of: 
 forming, on a substrate, a first laser element portion which oscillates laser light having a first wavelength;    forming, on said substrate, a second laser element portion which oscillates laser light having a second wavelength;    forming a front end face film having a uniform film thickness at once on front end faces of said first and second laser element portions by using ECR sputtering; and    forming a rear end face film having a uniform film thickness and comprising a plurality of thin films at once on rear end faces of said first and second laser element portions by using ECR sputtering.    
     
     
         7 . A method according to  claim 6 , wherein the step of forming said front end face film comprises forming a film having a reflectivity of 3 to 37%, and the step of forming said rear end face film comprises forming a film having a reflectivity of not less than 75%.  
     
     
         8 . A method according to  claim 6 , wherein the step of forming said front end face film comprises forming a film by using a low-refractive-index material having a refractive index n<1.8, and the step of forming said rear end face film comprises forming a film which comprises stacked layers of thin films made of a low-refractive-index material having a refractive index n<1.8 and thin films made of a high-refractive-index material having a refractive index n>1.9.  
     
     
         9 . A method according to  claim 6 , wherein the step of forming said front end face film comprises forming an Al 2 O 3  film, and the step of forming said rear end face film comprises forming stacked layers of thin films made of a low-refractive-index material selected from the group consisting of Al 2 O 3  and SiO 2  and thin films made of a high-refractive-index material selected from the group consisting of SiN 4  and Si.  
     
     
         10 . A method according to  claim 8 , wherein the step of forming said front end face film comprises forming an Al 2 O 3  film, and the step of forming said rear end face film comprises forming stacked layers of thin films made of a low-refractive-index material selected from the group consisting of Al 2 O 3  and SiO 2  and thin films made of a high-refractive-index material selected from the group consisting of SiN 4  and Si.