Patent ID: 8064780

Claim:
A receiving device comprising: a dispersion compensator that performs dispersion compensation on an input light by a variable dispersion compensation amount; a demodulator that demodulates the input light by causing delay and interference; a detector that detects an error of a control phase amount of the delay and the interference; an adjustor that adjusts the control phase amount to a predetermined phase amount, based on the detected error; a monitor that monitors an error state of a data signal that is obtained by demodulation by the demodulator; and a controller that controls the adjustor to change, when the error state is in a predetermined state, the control phase amount from the predetermined phase amount, determines whether a differential M-phase shift keying signal light, where M=2 n and n is a positive integer, is included in the input light based on whether an error of the control phase amount that is detected after the control phase amount is changed changes according to a change of the control phase amount, and controls the dispersion compensator to stop the dispersion compensation based on whether the differential M-phase shift keying signal light is included in the input light.