Patent ID: 8891972

Claim:
An optical receiving apparatus, comprising: a variable dispersion compensation unit configured to compensate for a wavelength dispersion of an inputted optical signal of a differential M-phase modulation scheme, where M=2n and n is a natural number; a delay interference unit configured to perform a delay interference process on the optical signal dispersion-compensated by the variable dispersion compensation unit, the delay interference process causing interference between a branch component delayed by one bit and an optical-phase-controlled branch component; a photoelectric converter configured to perform a photoelectric conversion on the optical signal from the delay interference unit, so as to output a demodulated electrical signal corresponding to the differential M-phase modulation scheme; a polarization control unit configured to control a polarization state of the optical signal inputted to the photoelectric converter; an error monitor unit configured to monitor a number of error occurrences of the electrical signal outputted from the photoelectric converter; and a control unit configured to control a dispersion compensation amount at the variable dispersion compensation unit and an optical phase control amount at the delay interference unit, based on information on the number of error occurrences from the error monitor unit, wherein the control unit is configured to adjust the polarization state of the optical signal inputted to the photoelectric converter to a first polarization state, in which errors are more likely to occur than in normal operation, by controlling the polarization control unit and then start control of the variable dispersion compensation unit and the delay interference unit, and upon completion of the control, is configured to adjust the polarization state of the optical signal to a second polarization state, in which errors are less likely to occur than in the first polarization state, by controlling the polarization control unit, the polarization control unit including: a polarization controller capable of converting a polarization state of an inputted optical signal to an arbitrary polarization state; a polarizer for transmitting one polarization component of orthogonal polarization components of an optical signal having passed through the polarization controller; and an optical power monitor unit for monitoring power of the optical signal having passed through the polarizer, wherein the control unit adjusts a polarization state of an optical signal inputted to the photoelectric converter to the first polarization state by controlling the polarization controller to maximize the power to be monitored by the optical power monitor unit.