Patent ID: 7860408

Claim:
An interferometer for demodulating a differential M-phase shift keying signal comprising: a planar lightwave circuit (PLC) type interferometer main body; a first heating portion that heats the PLC type interferometer main body; an intermediate member which has a higher stiffness than that of the PLC type interferometer main body and is bonded to the PLC type interferometer main body and the first heating portion while being sandwiched between the PLC type interferometer main body and the first heating portion; a second heating portion located adjacent to an optical waveguide included in the PLC type interferometer main body, wherein phase adjustment of the differential M-phase shift keying signal flowing through the PLC type interferometer main body is performed by a temperature control using the first heating portion, and phase adjustment finer than that made by using the first heating portion is performed by a temperature control using the second heating portion.