DIGITAL MULTI-CHANNEL NONLINEARITY COMPENSATION SCHEME FOR OPTICAL COHERENT COMMUNICATION

This application relates to a compensating apparatus for compensating nonlinear distortions induced on an optical signal during transmission through an optical link. The apparatus comprises an optical link interface configured to receive a sequence of first complex symbols (ax, ay) at a first wavelength (» a ) of the optical signal and to receive a sequence of second complex symbols (bx, by) at a second wavelength (» b ) of the optical signal. The apparatus also includes a symbol processing unit and a filtering unit. The symbol processing unit may be configured to process the second complex symbols (bx, by) using a nonlinear operation, thereby obtaining processed second complex symbols (d b , q b ). The filtering unit may be configured to linearly filter the processed second complex symbols (d b , q b ) to produce a second sequence of filter coefficients (f (ab) , g (ab) ) associated with inter-channel nonlinearity. The apparatus further comprises a perturbation calculating unit configured to generate a sequence of inter-nonlinear perturbation terms (”ax inter , ”ay inter ) associated with the received first complex symbols (ax, ay) based on the received first complex symbols (ax, ay) and the second sequence of filter coefficients (f (ab) , g (ab) ). The apparatus also comprises a compensating unit configured to remove the inter-nonlinear perturbation terms (”ax inter, ”ay inter ) from the corresponding first complex symbols (ax, ay) to compensate the nonlinear distortions induced on the first complex symbols (ax, ay) by the second complex symbols (bx, by).