Optical receiver and optical receiving method corresponding to differential M-phase shift keying system

An optical receiving apparatus comprising,

• a branching unit for supplying signal lights of almost equal power obtained by branching an input light,
• a delay adjusting unit for giving relative delay time difference according to a symbol duration of the differential M-phase shift keying modulated signal to a first signal light and a fourth signal light,
• a demodulating unit for demodulating at least two light signals through interference of respective signal lights of the first and second signal lights and the third and fourth signal lights, and
• at least two light detectors for converting said at least two light signals from said demodulating unit into electrical signals,
• 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 a relative delay time difference corresponding to symbol duration of said input light wavelength in said delay adjusting unit.

An optical apparatus, comprising:

• a plurality of interferometers, each interferometer having a plurality of interferometer arms with different optical path lengths;
• a branching unit coupling the plurality of interferometers or the arms of the plurality of interferometers;
• and
• an optical coupler coupling the plurality of interferometers, wherein
• operating points of the plurality of 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 symbol duration of a symbol of a differential M-phase shift keying modulated signal.