Patent ID: 8150219

Claim:
A waveguide-type optical interferometer including at least one input waveguide, an optical splitter connected to the input waveguide, at least one output waveguide, an optical combiner connected to the output waveguide, and at least two arm waveguides that provide a connection between the optical splitter and the optical combiner, the waveguide-type optical interferometer comprising: a first half-wave plate interposed at a midpoint of an optical path length of each of the at least two arm waveguides; and a second half-wave plate having an optic axis inclined at any one of 45° and −45° relatively to the first half-wave plate, and interposed in the at least two arm waveguides on any one of the input waveguide side and the output waveguide side of the at least two arm waveguides; wherein: the at least two arm waveguides are formed of two arm waveguides of a long arm waveguide and a short arm waveguide, and the first half-wave plate includes separate half-wave plates for the long arm waveguide and the short arm waveguide, respectively, the separate half-wave plates and the second half-wave plate form separate polarization rotators, respectively, the inclinations of optic axes of the respective separate half-wave plates are set so that the optic axes extend in the same direction or form an angle of 90°, and birefringence B is set so as to obtain the relationship m−0.25<α<m+0.20 (where m is an integer) for the value of α expressed by: α= B*ΔL /(2*λ)+Φ/2π where ΔL denotes an optical path difference between the long arm waveguide and the short arm waveguide; B denotes the birefringence of the waveguides; λ denotes a wavelength used in the interferometer; and Φ denotes a phase difference between the arm waveguides, provided that the phase difference Φ is set equal to 0° or 180°, when the inclinations of optic axes of the respective separate half-wave plates are set so that the optic axes extend in the same direction or form an angle of 90°.