Optical receiver and controlling method thereof, and optical transmission system

A controlling method in an optical receiver comprising:

• a variable dispersion compensating section that compensates wavelength dispersion of an input optical signal of a differential M-phase modulation format, where M=2n when n is a natural number;
• a delay interfering section that performs delay interference processing in which a one-bit delayed branched component and an optically phase-controlled branched component, of the optical signal dispersion-compensated by the variable dispersion compensating section, are made to interfere with each other;
• and a photoelectric converting section that performs photoelectric conversion detection with respect to an optical signal from the delay interfering section, to thereby output a demodulated electric signal corresponding to the differential M-phase modulation format;
• that monitors information related to an error rate of an electric signal output from the photoelectric converting section, and controls the dispersion compensation amount in the variable dispersion compensating section and the optical phase control amount in the delay interfering section, based on the monitor information,
• the method comprising deteriorating the signal-to-noise ratio of the optical signal input to the photoelectric converting section, to thereby realize a state in which the monitored information corresponds to a preset target error rate, and then starting control of the variable dispersion compensating section and the delay interfering section.

An optical transmission system comprising;

• an optical transmitter that generates an optical signal of a differential M-phase modulation format, where M=2n when n is a natural number, and outputs this to a transmission path, and an optical receiver that receives and processes the optical signal transmitted on the transmission path, wherein
• the optical receiver comprises:
• a variable dispersion compensating section that compensates wavelength dispersion of an input optical signal transmitted on the transmission path;
• a delay interfering section that performs delay interference processing in which a one-bit delayed branched component and an optically phase-controlled branched component, of the optical signal dispersion-compensated by the variable dispersion compensating section, are made to interfere with each other;
• a photoelectric converting section that performs photoelectric conversion detection with respect to an optical signal from the delay interfering section, to thereby output a demodulated electric signal corresponding to the differential M-phase modulation format;
• an error monitor section that monitors information relating to an error rate of the electric signal output from the photoelectric converting section;
• and
• a control section that controls a dispersion compensation amount in the variable dispersion compensating section and an optical phase control amount in the delay interfering section,
• and furthermore the control section transmits control information for decreasing the optical output level of the optical transmitter to the optical transmitter, to thereby realize a state in which the information monitored by the error monitor section corresponds to a preset target error rate, and then starts control of the variable dispersion compensating section and the delay interfering section, and transmits control information for returning the optical output level of the optical transmitter to the optical transmitter, by completing the control.