Patent ID: 7773652

Claim:
A gain-coupled distributed feedback semiconductor laser comprising: an optical waveguide through which laser light travels; a diffraction grating with an absorbing portion which selects laser light with a predetermined oscillation wavelength, located along the optical waveguide; a front facet covered with a first coating having a first reflectivity, located at a first end of the optical waveguide, where the laser light is emitted; and a rear facet coated with a second coating having a second reflectivity, higher than the first reflectivity, located at a second end of the optical waveguide, wherein the optical waveguide and the diffraction grating extend to the rear facet, the diffraction grating includes a phase shift region in which the period of the diffraction is shifted by a phase of λ/4, and distance between the phase shift region and the front facet is smaller than distance between the phase shift region and the rear facet.