Patent ID: 8737446

Claim:
A semiconductor laser, comprising: a gain region; a distributed Bragg reflector region including a diffraction grating; an end facet facing the distributed Bragg reflector region with the gain region arranged therebetween; a first ring resonator including a first ring-like waveguide and a first optical coupler having a first input port and a first output port, the first output port including a through port and a cross port; a second ring resonator including a second ring-like waveguide and a second optical coupler having second input port and a second output port, the second output port including a through port and a cross port; and an optical waveguide that is optically coupled to the end facet and extending in a predetermined optical-axis direction, wherein the first ring-like waveguide of the first ring resonator is optically coupled to the optical waveguide through the cross port of the first optical coupler, the second ring-like waveguide of the second ring resonator is optically coupled to the optical waveguide through the cross port of the second optical coupler, the through port of the first optical coupler of the first ring resonator and the through port of the second optical coupler of the second ring resonator are connected to each other in series by the optical waveguide, the distributed Bragg reflector region, the gain region, and the end facet constitute a laser cavity, the first, and second ring resonators have periodic transmittance peak wavelengths, the first ring resonator has a free spectral range different from a free spectral range of the second ring resonator, and at least one of the transmittance peak wavelengths of th second ring resonator is included in each transmission band of the transmittance peak wavelengths of the first ring resonator.