Semiconductor laser with varied-width waveguide and semiconductor laser module including the same

Abstract

A semiconductor laser outputs a laser light from an output facet of a waveguide having an index waveguide structure, via a lens system. The waveguide includes, in order from a rear facet opposite to the output facet, a first narrow portion, a wide portion that is wider than the first narrow portion, a second narrow portion narrower than the wide portion, a first tapered portion formed between the first narrow portion and the wide portion, which expands toward the wide portion, and a second tapered portion formed between the wide portion and the second narrow portion, which narrows toward the second narrow portion. Each of the first narrow portion, the wide portion, and the second narrow portion has a uniform width.

What is claimed is: 
     
         1 . A semiconductor laser that outputs a laser light from an output facet of a waveguide having an index waveguide structure, via a lens system, wherein
 the waveguide includes, in order from a rear facet opposite to the output facet,
 a first narrow portion, 
 a wide portion that is wider than the first narrow portion, 
 a second narrow portion narrower than the wide portion, 
 a first tapered portion formed between the first narrow portion and the wide portion, the first tapered portion expanding toward the wide portion, and 
 a second tapered portion formed between the wide portion and the second narrow portion, the second tapered portion narrowing toward the second narrow portion, and 
   each of the first narrow portion, the wide portion, and the second narrow portion has a uniform width.   
     
     
         2 . The semiconductor laser according to  claim 1 , wherein an inclination angle θ represented by θ=arctan [(ΔW/2)/Lt2] is 0.6 degrees or less, where ΔW is difference between a width of the wide portion and a width of the second narrow portion in the waveguide and Lt2 is a length of the second tapered portion. 
     
     
         3 . The semiconductor laser according to  claim 2 , wherein the inclination angle θ satisfies
     Ln 2≧106θ−0.00681, where 0.47<θ≦0.60,
 
     Ln 2≧317θ−100, where 0.32<θ≦0.47, and
 
     Ln 2≧0, where θ≦0.32,
 
 
       where Ln2 is length of the second narrow portion. 
     
     
         4 . The semiconductor laser according to  claim 1 , wherein a length of the first narrow portion is equal to or longer than 30% of a cavity length of a resonator that is made up with the output facet and the rear facet. 
     
     
         5 . The semiconductor laser according to  claim 1 , wherein a difference between a width of the wide portion and a width of the second narrow portion is in a range of 1.0 micrometer to 3.3 micrometers. 
     
     
         6 . The semiconductor laser according to  claim 1 , wherein a length of the second tapered portion is equal to or longer than 50 micrometers. 
     
     
         7 . The semiconductor laser according to  claim 1 , wherein a cavity length of a resonator that is made up with the output facet and the rear facet is equal to or longer than 1000 micrometers. 
     
     
         8 . The semiconductor laser according to  claim 1 , further comprising a current non-injection structure that prevents a current from flowing into the second portion and at least a part of the second tapered portion. 
     
     
         9 . The semiconductor laser according to  claim 1 , wherein the waveguide further includes
 a third narrow portion formed on the rear facet side, the third narrow portion having a uniform width approximately same as a width of the second narrow portion, and   a third tapered portion formed between the third narrow portion and the first narrow portion, the third tapered portion narrowing toward the first narrow portion.   
     
     
         10 . The semiconductor laser according to  claim 1 , wherein the semiconductor laser is a distributed feedback laser. 
     
     
         11 . The semiconductor laser according to  claim 1 , wherein the semiconductor laser is a distributed feedback laser employing a phase-shift diffraction grating. 
     
     
         12 . A semiconductor laser that outputs a laser light from an output facet of a waveguide having an index waveguide structure, via a lens system, wherein
 the waveguide includes, in order from a rear facet opposite to the output facet,
 a first narrow portion, 
 a wide portion wider than the first narrow portion, 
 a first tapered portion formed between the first narrow portion and the wide portion, the first tapered portion expanding toward the wide portion, and 
 a second tapered portion narrowing from the side portion toward the output facet, 
   each of the first narrow portion and the wide portion has a uniform width, and   an inclination angle θ represented by θ=arctan [(ΔW/2)/Lt2] is 0.32 degrees or less, where ΔW is difference between a width of the wide portion and a width of the second tapered portion on the output facet side and Lt2 is length of the second tapered portion.   
     
     
         13 . A semiconductor laser module comprising:
 a semiconductor laser that outputs a laser light from an output facet of a waveguide having an index waveguide structure;   a coupling target to which the laser light is to be coupled; and   a lens system that couples the laser light to the coupling target, wherein   the waveguide includes, in order from a rear facet opposite to the output facet,
 a first narrow portion, 
 a wide portion that is wider than the first narrow portion, 
 a second narrow portion narrower than the wide portion, 
 a first tapered portion formed between the first narrow portion and the wide portion, the first tapered portion expanding toward the wide portion, and 
 a second tapered portion formed between the wide portion and the second narrow portion, the second tapered portion narrowing toward the second narrow portion, and 
   each of the first narrow portion, the wide portion, and the second narrow portion has a uniform width.   
     
     
         14 . The semiconductor laser module according to  claim 13 , wherein
 the coupling target is an optical fiber, and   optical power of a laser light output from the optical fiber is equal to or greater than 300 milliwatts.