Wavelength tunable semiconductor laser having two difractive grating areas

Abstract

A semiconductor laser has a first diffractive grating area. The first diffractive grating area has a plurality of segments. Each segment has a first area including a diffractive grating and a second area that is space area combined to the first area. Optical lengths of at least two of the second areas are different from each other. A refractive-index of each of the segments are changeable.

What is claimed is: 
     
         1 . A semiconductor laser comprising:
 a first diffractive grating area that has a plurality of segments; and   a second diffractive grating area that has another plurality of segments,   wherein each of the plurality of segments of said first diffractive grating area has a first area including a diffractive grating and a second area that is a space area combined to the first area, optical lengths of at least two of the second areas being different from each other, and a refractive-index of each of the segments being changeable,   wherein each of the plurality of segments of said second diffractive grating area has a first area including a diffractive grating and a second area that is a space area combined to the first area, optical lengths of at least two of the second areas being different from each other, and a refractive-index of each of the segments being changeable, and   wherein a length of the first area is shorter than a length of the second area.   
     
     
         2 . The semiconductor laser as claimed in  claim 1 , wherein the first diffractive grating area or the second diffractive grating area has a gain region. 
     
     
         3 . The semiconductor laser as claimed in  claim 1  further comprising a gain region between the first diffractive grating area and the second diffractive grating area. 
     
     
         4 . The semiconductor laser as claimed in  claim 1 , wherein a minimum difference between the optical lengths of the second areas is within 1 to 6% of an average optical length of the second areas in the first diffractive grating area or/and the second diffractive grating area. 
     
     
         5 . The semiconductor laser as claimed in  claim 1  wherein minimum differences of the optical lengths between each of the second areas of the first diffractive grating area or/and the second diffractive grating area are equal to each other. 
     
     
         6 . The semiconductor laser as claimed in  claim 1 , wherein the segments of the first diffractive grating area or/and the second diffractive grating area are arranged in an ascending order or a descending order of optical length. 
     
     
         7 . The semiconductor laser as claimed in  claim 1 , wherein a light absorption area or a light amplification area is provided at an end face of the semiconductor laser. 
     
     
         8 . The semiconductor laser as claimed in  claim 1  further comprising a heater controlling a refractive-index of the segments of the first diffractive grating area or the second diffractive grating area. 
     
     
         9 . The semiconductor laser as claimed in  claim 1  further comprising a phase control area controlling a phase of a light between the first diffractive grating area and the second diffractive grating area.