Carrier phase estimator for non-linear impairment monitoring and mitigation in coherent optical systems

A method for determining a plurality of estimates of a carrier phase of a signal transmitted over an optical transmission channel of an optical fiber, the method comprising:

• receiving, at a receiver, a plurality of samples of the signal at succeeding time instances;
• wherein
• the plurality of signal samples is associated with a modulation scheme, which allows a number of possible data phase values, and the carrier phase;
• at a corresponding transmitter, the plurality of signal samples has been encoded using the modulation scheme, modulated onto an optical carrier signal having the carrier phase and transmitted over the optical transmission channel;
• the plurality of signal samples comprises a plurality of signal amplitudes and signal phases, respectively;
• the plurality of signal phases comprises a plurality of data phases and a plurality of residual phases, respectively;
• the plurality of residual phases is associated with the carrier phase;
• canceling (401) the plurality of data phases from the plurality of signal phases by taking into account the modulation scheme;
• thereby yielding the plurality of residual phases;
• determining (301) a second lag value (611);
• and
• filtering (402) the plurality of residual phases with a filter comprising a number of filter taps corresponding to two times the second lag value (611);
• thereby yielding a plurality of filtered residual phases, associated with the plurality of estimates of the carrier phase at the succeeding time instances.

A system configured to provide a measure of the non-linearity of an optical transmission channel of an optical fiber, the system comprising:

• a reception unit configured to provide a plurality of signal samples at succeeding time instances;
• wherein
• the plurality of signal samples is associated with a modulation scheme, which allows a number of possible data phase values, and a carrier phase;
• at a corresponding transmitter, the plurality of signal samples has been encoded using the modulation scheme, modulated onto an optical carrier signal having the carrier phase and transmitted over the optical transmission channel;
• the plurality of signal samples comprises a plurality of signal amplitudes and signal phases, respectively;
• the plurality of signal phases comprises a plurality of data phases and a plurality of residual phases, respectively;
• the plurality of residual phases is associated with the carrier phase;
• a data phase cancellation unit (401) configured to cancel the plurality of data phases from the plurality of signal phases by taking into account the modulation scheme;
• thereby yielding the plurality of residual phases;
• and
• a carrier phase statistics determination unit (301) configured to determine a set of autocorrelation values of the plurality of residual phases for a set of lag values, respectively;
• thereby yielding the measure for the non-linearity of the optical transmission channel.

A carrier phase estimation unit (221) configured to provide a plurality of estimates of a carrier phase at succeeding time instances, the unit (221) comprising

• a reception unit configured to provide a plurality of signal samples at the succeeding time instances;
• wherein
• the plurality of signal samples is associated with a modulation scheme, which allows a number of possible data phase values, and the carrier phase;
• the plurality of signal samples has been encoded using the modulation scheme, modulated onto an optical carrier signal having the carrier phase and transmitted over an optical transmission channel;
• the plurality of signal samples comprises a plurality of signal amplitudes and signal phases, respectively;
• the plurality of signal phases comprises a plurality of data phases and a plurality of residual phases, respectively;
• the plurality of residual phases is associated with the carrier phase;
• a data phase cancellation unit (401) configured to cancel the plurality of data phases from the plurality of signal phases by taking into account the modulation scheme;
• thereby yielding the plurality of residual phases;
• a carrier phase statistics determination unit (301) configured to determine a second lag value (611);
• and
• a filtering unit (402) configured to filter the plurality of residual phases with a filter comprising a number of filter taps corresponding to two times the second lag value (611);
• thereby yielding a plurality of filtered residual phases, associated with the plurality of estimates of the carrier phase at the succeeding time instances.

An optical receiver (300), comprising:

• a coherent receiver (100) configured to receive an in-phase and a quadrature component of an optical signal;
• an optical detection unit (121, 122) configured to convert the optical signal into an electrical signal;
• a plurality of analog-to-digital converters (123, 124) configured to convert the in-phase and the quadrature component of the electrical signal into a digital signal comprising a plurality of signal samples at succeeding time instances;
• wherein the plurality of signal samples is associated with a carrier phase;
• a carrier phase estimation unit (221) configured to provide a plurality of estimates of the carrier phase at the succeeding time instances;
• and
• a carrier phase compensation unit (222) configured to modify the plurality of signal samples based on the plurality of estimates of the carrier phase.