Patent ID: 7843986

Claim:
A tunable laser device, comprising: planar lightwave circuit; and a light-supplying part for supplying light to the optical filter via the first optical waveguide of the planar lightwave circuit; wherein said planar lightwave circuit, comprising: a first optical waveguide and a second optical waveguide; an optical filter formed by coupling a plurality of ring resonators of different optical path lengths to output and input light via the first optical waveguide; a light reflecting part which returns the light transmitted through the optical filter to the optical filter via the second optical waveguide; a phase shifter to change a phase of light that transmits through the optical filter; and a plurality of optical coupling parts which optically couple the plurality of ring resonators to each other and optically couple the first optical waveguide, the optical filter, and the second optical waveguide, wherein at least one of the optical coupling parts is formed with an asymmetrical Mach-Zehnder interferometer and the phase shifter is a thin-film heater which changes a temperature of the optical waveguides which configure the ring resonators, wherein said tunable laser device, further comprising, a light-receiving element which detects light from at least one of the plurality of ring resonators via a through port; and a control unit which adjusts an electric current amount supplied to the phase shifter in such a manner that a light amount detected at the light-receiving element becomes small.