Patent ID: 9602207
Date: 2017-03-21
CPC Classifications: H04B,H04L

Claim:
1. A method of compensating polarization dependent loss (PDL) in an optical communications network comprising a transmitter and a coherent optical receiver, the method comprising: transmitting, by the transmitter, an optical signal having a controllable polarization state, the optical signal carrying symbols modulated onto two orthogonal transmitted polarizations; receiving, by the coherent optical receiver, the optical signal and processing orthogonal polarizations of the received optical signal to recover symbol estimates of the symbols modulated onto the two orthogonal transmitted polarizations; computing from the symbol estimates, by the coherent optical receiver, an estimate representative of a noise polarization dependent loss of the received optical signal; transmitting, by the coherent optical receiver, the computed estimate to the transmitter; controlling, by the transmitter, the polarization state using the computed estimate; and applying, by a decorrelation block of the coherent optical receiver, a decorrelation matrix to the symbol estimates to generate a set of decorrelated signals corresponding to the symbol estimates, thereby reducing a noise correlation that is a correlation between noise in the symbol estimates of the symbols modulated onto a first of the orthogonal transmitted polarizations and noise in the symbol estimates of the symbols modulated onto a second of the orthogonal transmitted polarizations.