Patent ID: 7606504

Claim:
An optical receiving apparatus, comprising: first and fourth optical waveguides; second and third optical waveguides giving relative delay time differences corresponding to a symbol of a differential M-phase shift keying modulated signal for the first and fourth optical waveguides, respectively; a branching unit supplying almost equal powers branched from input signal light inputted to the first to fourth optical waveguides; a demodulating unit demodulating at least two light signals through interference of signal lights between said first to second optical waveguides and between said third to fourth optical waveguides; at least two optical detectors converting at least two light signals from said demodulating unit into electrical signals; and a light path length varying unit varying each light path length of two optical waveguides being arranged through selection of combinations of said first and third optical waveguides, said first and fourth optical waveguides, and said second and third optical waveguides in a region when the wavelength of said signal light is varied, wherein operating points of two delay interferometers are set to a predetermined communication rate, between a minimum communication rate and a maximum communication rate of multi-rate communication, based on the relative delay time differences corresponding to a symbol duration of said symbol.