Optical communication device

An optical communication device, comprising:

• a transmitter to transmit optical signals including polarization multiplexed signals multiplexing signals of a first polarization on which a burst signal including, at a beginning thereof, a pilot sequence having a single frequency component of a first frequency, is generated and a second polarization orthogonal to the first polarization, on which a burst signal including, at a beginning thereof, a pilot sequence having a single frequency component of a second frequency different from the first frequency, is generated;
• and
• a receiver to receive the optical signals from the transmitter;
• wherein the receiver includes:
• a coherent light receptor to output a coherent detection signal by performing conversion into an electrical signal by allowing the optical signals transmitted from the transmitter and local light to interfere with each other;
• an A/D converter to convert the coherent detection signal output from the coherent light receptor into a digital signal;
• a pilot sequence detector to detect the pilot sequence from an output signal of the A/D converter;
• a polarization estimator to, when the pilot sequence detector detects the pilot sequence, estimate a polarization state of signals of the first polarization at the receiver by performing maximal ratio combining on H polarization components and V polarization components at the first frequency in detected pilot sequences, and estimate a polarization state of signals of the second polarization at the receiver by performing maximal ratio combining on H polarization components and V polarization components at the second frequency in the detected pilot sequences;
• an adaptive equalizer to demultiplex signals of the first polarization and signals of the second polarization from the output signal of the A/D converter on a basis of the polarization states estimated by the polarization estimator;
• a coefficient updater to update a coefficient of the adaptive equalizer using, as an initial value, setting for demultiplexing a signal of the first polarization and a signal of the second polarization on a basis of the polarization states estimated by the polarization estimator, according to results calculated by using constant modulus algorithm;
• a phase estimator to estimate and compensate a phase of a signal of the first polarization and a signal of the second polarization, demultiplexed by the adaptive equalizer;
• and
• a decoder to determine and decode a signal of the first polarization and a signal of the second polarization, of which phase has been compensated by the phase estimator.