OPTICAL TRANSMITTER

PROBLEM TO BE SOLVED: To obtain an inexpensive optical transmitter having characteristics stabilized over a wide temperature range by providing an insulator diffraction grating comprising layers of oxidized compound semiconductor formed at same period as a diffraction grating on the boundary of the diffraction grating and a clad layer. SOLUTION: A distributed feedback semiconductor laser comprises an active layer 204 emitting light, an upper p-type clad layer 209 for confining light emitted from the active layer 204, an upper optical guide layer 205 provided between the active layer 204 and the clad layer 209, a spacer layer 206 formed with a diffraction grating for coupling refractive index, and a carrier block layer 207 provided on the boundary of the spacer layer 206 and the clad layer 209 formed on a semiconductor substrate 201. The carrier block layer 207 is formed as an insulator diffraction grating comprising a grating of insulation layer. Since the insulator diffraction grating is formed above the diffraction grating for coupling refractive index, periods of grating are matched each other.