Distributed reflector and wavelength-tunable semiconductor laser

A distributed reflector semiconductor laser having an optical waveguide comprising:

• an active waveguide layer defining an active waveguide region,
• at least one inactive waveguide layer optically connected to said active waveguide layer, defining an inactive region having a refractive index,
• a diffractive grating provided in at least a portion of said inactive region;
• a distributed reflector constituted by said diffractive grating, said active region and said inactive region;
• said active region having an optical gain to light having a wavelength which said distributed reflector reflects;
• said active region having an optical amplification action and said distributed reflector having a reflection action, and together causing lasing at at least one of reflection wavelengths in said distributed reflector;
• said diffractive grating in said at least one distributed reflector having a plurality of repeating unit regions each having a constant length, thus forming a modulation period, and at least one parameter that determines an optical reflectivity of said diffractive grating varying depending on its position in each of said repeating unit regions along a direction of optical transmission in said distributed reflector;
• said diffractive grating extending by at least two modulation periods;
• and
• means for electrically controlling said refractive index of said inactive region.

A distributed feed back semiconductor laser having an optical waveguide comprising:

• an active waveguide layer defining an active region having a refractive index,
• an inactive waveguide layer optically connected to said active waveguide layer, defining an inactive region,
• a diffractive grating provided in at least a portion of said active region;
• a distributed reflector constituted by said diffractive grating, said active region and said inactive region;
• said active region having an optical gain to light having a wavelength which said distributed reflector reflects;
• said active region having an optical amplification action and said distributed reflector having a reflection action, and together causing lasing at least one of reflection wavelengths in said distributed reflector;
• said diffractive grating in said at least one distributed reflector having a plurality of repeating unit regions each having a constant length, thus forming a modulation period, and at least one parameter that determines an optical reflectivity of the diffractive grating varying depending on its position in each of said repeating unit regions along a direction of optical transmission in the distributed reflector;
• said diffractive grating extending by at least two modulation periods;
• and
• means for electrically controlling said refractive index of said inactive region.