Adaptive crossing frequency domain equalization (FDE) in digital PolMux coherent systems

1. 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 of the four digital electrical signals that 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; and

estimating filter coefficients using a blind/training based methodology.