Adaptive crossing frequency domain equalization (fde) in digital polmux coherent systems

A method for providing adaptive crossing frequency domain equalization chromatic dispersion compensation, polarization mode dispersion compensation and polarization demultiplexing of a polarization multiplexed (PolMux) optical signal comprising the steps of:

• applying the PolMux optical signal to an optical hybrid such that four output signals X′I, X′Q, Y′I, Y′Q are produced wherein X′ and Y′ represent two random polarizations orthogonal to one another and I and Q represent two orthogonal phases;
• generating four digital electrical signals from the four output signals;
• applying the four digital electrical signals to a digital signal processor wherein the following steps are performed:
• performing an adaptive crossing frequency domain equalization the four digital electrical signals have any chromatic dispersion and polarization mode dispersion compensated, thereby producing two compensated complex signals;
• compensating for any frequency offset exhibited by the two compensated signals;
• mitigating any noise exhibited by the two frequency offset compensated signals;
• and
• demodulating X and Y data from the two complex signals such that two signals Pol-X data and Pol-Y data are produced.