Optical communication receiving device and frequency offset compensation method
A receiving device that converts, to a digital signal, a signal in which signal light from an optical transmission path and local oscillation light are mixed, so as to perform digital signal processing, the optical communication receiving device comprising: a frequency offset compensation unit configured to calculate a frequency offset of the digital signal and to, based on the frequency offset, compensate for a phase of the digital signal; a carrier phase recovery unit configured to calculate a carrier phase of the digital signal whose phase is compensated for in the frequency offset compensation unit; and a residual frequency offset detection unit configured to calculate an average of differences in the carrier phase, and to output the average as a residual frequency offset, wherein the frequency offset compensation unit is configured to correct the frequency offset using the residual frequency offset output by the residual frequency offset detection unit.
1. An optical communication receiving device that converts, to a digital signal, a signal in which signal light from an optical transmission path and local oscillation light are mixed, so as to perform digital signal processing, the optical communication receiving device comprising:
a frequency offset compensator configured to calculate a frequency offset of the digital signal and to, based on the frequency offset, compensate for a phase of the digital signal;
a carrier phase recoverer configured to calculate a carrier phase of the digital signal whose phase is compensated for in the frequency offset compensator; and
a residual frequency offset detector configured to calculate an average of differences in a carrier phase of each of a plurality of symbols, and to output the average as a residual frequency offset,
wherein the frequency offset compensator is configured to correct the frequency offset using the residual frequency offset output by the residual frequency offset detector, and
wherein the residual frequency offset detector is configured to set a difference in the carrier phase to zero when an absolute value of the difference in the carrier phase exceeds a predetermined value.
2. The optical communication receiving device according to claim 1 , wherein the residual frequency offset detector is configured to set a difference in the carrier phase to a predetermined positive value when the difference in the carrier phase exceeds the positive predetermined value, and to set the difference in the carrier phase to a predetermined negative value when the difference in the carrier phase is less than the predetermined negative value.
3. A frequency offset compensation method, comprising:
calculating a frequency offset of a digital signal obtained by converting a signal in which signal light from an optical transmission path and local oscillation light are mixed, and, based on the frequency offset, compensating for a phase of the digital signal;
calculating a carrier phase of the digital signal the phase of which is compensated for;
calculating an average of differences in a carrier phase of each of a plurality of symbols and outputting the average as a residual frequency offset; and
correcting the frequency offset using the output residual frequency offset,
wherein a difference in the carrier phase is set to zero when an absolute value of the difference in the carrier phase exceeds a predetermined value.
4. The frequency offset compensation method according to claim 3 , wherein a difference in the carrier phase is set to a predetermined positive value when the difference in the carrier phase exceeds the predetermined positive value, and the difference in the carrier phase is set to a predetermined negative value when the difference in the carrier phase is less than the predetermined negative value.
5. The optical communication receiving device according to claim 1 , wherein an amount of each of the differences in the carrier phase is recorded in succession, and a phase skip component is corrected through unwrapping.