Optical semiconductor device and method of controlling the same

An optical semiconductor device comprising:

• a waveguide that has one or more first segments, one or more second segments and a plurality of third segments,
• the first segment having a region that includes a diffractive grating and another region that is a space region combined to the region,
• the second segment having a region that includes a diffractive grating and another region that is a space region combined to the region,
• a length of the second segment being different from that of the first segment,
• the third segment having a region that includes a diffractive grating and another region that is a space region combined to the region,
• a length of the third segment being shown as L3=L1+(L2−L1)×K1 in which 0.3≦K1≦0.7, L1 is a length of the first segment, L2 is a length of the second segment, and L3 is a length of the third segment;
• a refractive index control portion that controls refractive index of the first segment through the third segments;
• and
• a controller controlling the refractive index control portion.