US Patent 7843986 Planar lightwave circuit and tunable laser device having the same

To prevent the property of an optical filter from being changed even if there is a change in a gap of directional couplers generated due to variations in manufacturing conditions so as to improve the yield. A tunable laser device includes a PLC and an SOA. The PLC includes: optical waveguides; an optical filter; a loop mirror; thin-film heaters; and asymmetrical MZIs. Optical coupling parts within the PLC are formed with the asymmetrical MZIs, so that there is no change generated in the property of the optical filter even if there is a change generated in a gap of the directional couplers due to variations in the manufacturing conditions. Therefore, the yield can be improved.