Abstract: A distributed feedback semiconductor laser (DFB laser) in which light feedback is performed by using a diffraction grating, and in which influence of external feedback noises can be decreased to suppress fluctuation of an optical output. The DFB laser comprises a diffraction grating structure portion which constitutes a resonator and which is divided into a plurality of regions along the longitudinal direction of the resonator, and one or more phase shift portions each disposed between adjacent regions of the diffraction grating structure portion, wherein total phase shift obtained by all of the phase shift portions has a quantity corresponding to &lgr;/n, where &lgr; is an oscillation wavelength, and n is an integer larger than 4 (n>4) and less than or equal to 16 (n≦16). The total phase shift may have a quantity corresponding to a value within a range between &lgr;/5 and &lgr;/8.

Abstract: A distributed feedback semiconductor laser includes a semiconductor substrate, a diffraction grating, an optical guide layer, an active layer, a cladding layer, first and second electrodes, and an antireflection coating film. The diffraction grating is formed on the semiconductor substrate and constitutes a resonator. The diffraction grating has a &lgr;/4 phase-shift region for changing a phase of light by &lgr;/4. The optical guide layer is formed on the diffraction grating. The active layer is formed on the optical guide layer to correspond to a region other than the &lgr;/4 phase-shift region. The cladding layer is formed on the active layer and the optical guide layer. The first electrode is formed on the cladding layer through a cap layer. The second electrode is formed on a lower surface of the semiconductor substrate and adapted to cause distributed feedback of light. The antireflection coating film is formed on each of front and rear end faces of the resonator.

Abstract: A distributed feedback semiconductor laser (DFB laser) in which light feedback is performed by using a diffraction grating, and in which influence of external feedback noises can be decreased to suppress fluctuation of an optical output. The DFB laser comprises a diffraction grating structure portion which constitutes a resonator and which is divided into a plurality of regions along the longitudinal direction of the resonator, and one or more phase shift portions each disposed between adjacent regions of the diffraction grating structure portion, wherein total phase shift obtained by all of the phase shift portions has a quantity corresponding to &lgr;/n, where &lgr; is an oscillation wavelength, and n is an integer larger than 4 (n>4) and less than or equal to 16 (n≦16). The total phase shift may have a quantity corresponding to a value within a range between &lgr;/5 and &lgr;/8.

Abstract: A distributed feedback semiconductor laser (DFB laser) in which light feedback is performed by using a diffraction grating, and in which influence of external feedback noises can be decreased to suppress fluctuation of an optical output. The DFB laser comprises a diffraction grating structure portion which constitutes a resonator and which is divided into a plurality of regions along the longitudinal direction of the resonator, and one or more phase shift portions each disposed between adjacent regions of the diffraction grating structure portion, wherein total phase shift obtained by all of the phase shift portions has a quantity corresponding to &lgr;/n, where &lgr; is an oscillation wavelength, and n is an integer larger than 4 (n>4). The total phase shift may have a quantity corresponding to a value within a range between &lgr;/5 and &lgr;/8.

Abstract: A semiconductor optical functional device is divided into two regions of a first region 1 and a second region 2 adjacent to each other in a longitudinal direction of a semiconductor optical waveguide. The first region 1 is provided with a region including an MQW structure in which a compressive strain is introduced, and the second region 2 is provided with a region including an MQW structure in which a tensile strain is introduced. Electrodes 3 and 4 formed separately and independently from each other are respectively disposed on the first region 1 and the second region 2, and bias voltages applied to the electrodes 3 and 4 are adjusted so that transmissivities for light having a TE mode component and light having a TM mode component are independently controlled.

Abstract: The waveguide of a distributed feedback laser is divided into first and second regions along a dividing line normal to the length of the waveguide. A phase shift is introduced to an interface between these regions so that the first region defines a gain-coupled diffraction grating structure when a first electric field is applied to it and the second region defines a loss-coupled diffraction grating structure when a second electric field opposite to the first electric field is applied. The former structure has a distribution of energy gains at periodic intervals and the latter structure has a distribution of energy absorptions at the same periodic intervals. One of the energy absorptions adjacent the dividing line is contiguous with one of the energy gains adjacent the dividing line. The energy gains and the energy absorptions occur at intervals equal to one-half wavelength of the output laser beam and the phase shift between the two regions is equal to a quarter wavelength of the laser beam.