An optical semiconductor apparatus includes at least two semiconductor laser portions each having a light waveguide with an active layer and a distributed reflector, and a stimulating unit for independently stimulating the active layers of the light waveguides. The semiconductor laser portions are serially arranged in a light propagation direction. The light waveguides are constructed such that a difference between propagation constants for two different polarization modes in one of the waveguides is different from a difference between propagation constants for the two different polarization modes in the other of the waveguides. When one of injection of a modulation current signal into or application of a modulation voltage to the optical semiconductor apparatus, an oscillation state can be switched between a state in which Bragg wavelengths for one of the two different polarization modes coincide with each other between the light waveguides and a state in which Bragg wavelengths for the other of the two different polarization modes coincide with each other between the light waveguides.