Linear dispersion polarization-time codes and equalization in polarization multiplexed coherent optical system

An optical communication apparatus comprising:

• a receiver configured to receive two sequences of digital signals in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital signal per polarization is received in each of the plurality of time slots;
• a digital signal processor comprising:
• a pair of frequency-domain equalizers configured to filter the two sequences of digital signals in the frequency domain to generate two frequency-domain equalized sequences;
• and
• a multiple-input and multi-output (MIMO) finite impulse response (FIR) equalizer configured to:
• divide each of the two frequency-domain equalized sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital signals received in two consecutive time slots;
• and
• adaptively equalize the four digital signals of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors.