Abstract: A length L1 of a first distributed Bragg reflector in a waveguide direction, a length L2 of a distributed feedback active region in the waveguide direction, a length L3 of a second distributed Bragg reflector in the waveguide direction, and a position xps of a phase shift portion are set to satisfy correlations of xps=L1+L2×?, L2(1??)+L3>xps, and 0.5<?<1. Further, the position xps is a position of the phase shift portion in the waveguide direction with an end portion thereof on the first distributed Bragg reflector side set as an origin.

Abstract: A semiconductor laser includes an active region, a first distributed-Bragg-reflector region disposed contiguously with the active region, and a second distributed-Bragg-reflector region. The first distributed-Bragg-reflector region is formed contiguously with one side of the active region in a waveguide direction and includes a first diffraction grating. The second distributed-Bragg-reflector region is formed contiguously with to the other side of the active region in the waveguide direction and includes a second diffraction grating. The first diffraction grating includes recessed portions formed through a diffraction grating layer formed in the first distributed-Bragg-reflector region and convex portions adjacent to the recessed portions. The diffraction grating layer is made of a dielectric material.

Abstract: A semiconductor laser includes a distributed feedback active region and two distribution Bragg reflecting mirror regions which are arranged to be continuous with the distributed feedback active region. The distributed feedback active region has an active layer which is composed of a compound semiconductor and a first diffraction grating. The first diffraction grating is composed of a recessed portion which is formed to extend through a diffraction grating layer formed on the active layer and a projection portion which is adjacent to the recessed portion.