An optical signal equalisation method comprising: receiving, at a signal processing unit, an input sequence of digital signal samples corresponding with an optical signal transmitted via an optical fibre link from a transmitter to a receiver; wherein the method further comprises: the signal processing unit processing the input sequence of digital signal samples to compute a distortion-mitigated sequence of output digital signal samples, said processing comprising, for each one of a plurality of segments of the optical fibre link proceeding sequentially from an initial segment associated with the receiver to a final segment associated with the transmitter: computing a first linear compensated signal by processing a segment input signal using a first linear backpropagation computational model of the segment; computing a nonlinear compensated signal by processing the first linear compensated signal using a nonlinear backpropagation computational model of the segment according to which a nonlinear compensation signal having a predetermined bandwidth limitation is computed and applied to the first linear compensated signal; and providing a segment output signal based upon the nonlinear compensated signal, outputting the distortion-mitigated sequence of output digital signal samples, wherein the segment input signal of the initial segment comprises the input sequence of digital signal samples, the segment input signal of each subsequent segment comprises the preceding segment output signal, and the distortion-mitigated sequence of digital signal samples comprises the segment output signal of the final segment. receiving, at a signal processing unit, an input sequence of digital signal samples corresponding with an optical signal transmitted via an optical fibre link from a transmitter to a receiver; wherein the method further comprises: the signal processing unit processing the input sequence of digital signal samples to compute a distortion-mitigated sequence of output digital signal samples, said processing comprising, for each one of a plurality of segments of the optical fibre link proceeding sequentially from an initial segment associated with the receiver to a final segment associated with the transmitter: computing a first linear compensated signal by processing a segment input signal using a first linear backpropagation computational model of the segment; computing a nonlinear compensated signal by processing the first linear compensated signal using a nonlinear backpropagation computational model of the segment according to which a nonlinear compensation signal having a predetermined bandwidth limitation is computed and applied to the first linear compensated signal; and providing a segment output signal based upon the nonlinear compensated signal, outputting the distortion-mitigated sequence of output digital signal samples, the signal processing unit processing the input sequence of digital signal samples to compute a distortion-mitigated sequence of output digital signal samples, said processing comprising, for each one of a plurality of segments of the optical fibre link proceeding sequentially from an initial segment associated with the receiver to a final segment associated with the transmitter: computing a first linear compensated signal by processing a segment input signal using a first linear backpropagation computational model of the segment; computing a nonlinear compensated signal by processing the first linear compensated signal using a nonlinear backpropagation computational model of the segment according to which a nonlinear compensation signal having a predetermined bandwidth limitation is computed and applied to the first linear compensated signal; and providing a segment output signal based upon the nonlinear compensated signal, outputting the distortion-mitigated sequence of output digital signal samples, wherein the segment input signal of the initial segment comprises the input sequence of digital signal samples, the segment input signal of each subsequent segment comprises the preceding segment output signal, and the distortion-mitigated sequence of digital signal samples comprises the segment output signal of the final segment.