Patent ID: 8379300

Claim:
A wavelength-variable light source configured to vary a wavelength of output lasing light, the wavelength-variable light source comprising: a 3-dB directional coupler including two input paths and two output paths; a closed loop-type optical circuit formed by connecting ends of the two output paths of the 3-dB directional coupler; at least two resonators cascaded together so as to form a part of the closed loop-type optical circuit and having different resonance wavelength periods; an optical amplifier including one end which is optically connected to one of the input path ends of the 3-dB directional coupler, and to another end from which the lasing light is output; a reflecting structure formed at the other end of the optical amplifier and having a predetermined reflection rate a non-reflecting structure formed at the other input path end of the 3-dB directional coupler; and a resonance wavelength variation element configured to vary the resonance wavelength of at least one of the at least two resonators.