Signal equalizer in a coherent optical receiver

A signal equalizer for compensating impairments of an optical signal received through a link of a high speed optical communications network, the signal equalizer comprising:

• means for computing at least one set of compensation vectors for compensating at least two distinct types of impairments;
• a frequency domain processor coupled to receive respective raw multi-bit in-phase (I) and quadrature (Q) sample streams of each received polarization of the optical signal, the frequency domain processor comprising:
• for each received polarization:
• a respective Fast Fourier Transform (FFT) block connected to receive the raw multi-bit sample streams of the received polarization, the FFT block being operative to compute a respective complex-value array representative of a frequency-domain spectrum of the received polarization, a width of the array being selected based on an expected maximum chromatic dispersion of the received optical signal;
• and
• a respective transpose-and-add block for adding the complex-value array to a transposed version of itself to generate a corresponding intermediate array;
• a cross-compensation block for digitally processing the respective intermediate arrays of each of the received polarizations to generate a set of modified arrays, each modified array being representative of a frequency-domain spectrum of a respective one of the transmitted polarizations;
• and
• a respective Inverse Fast Fourier transform (IFFT) block for processing each modified array to generate the multi-bit estimates of symbols modulated onto the corresponding transmitted polarization of the optical signal.