Method and system for non-linearity compensation in optical transmission systems

An equaliser for equalisation of a signal transmitted via an optical fibre link from a transmitter to a corresponding receiver, comprising:

• a digital signal processor;
• and
• at least one memory device operatively associated with the digital signal processor, wherein:
• the memory device contains parameters defining a backpropagation computational model of the optical fibre link, said backpropagation computational model comprising a plurality of sequential model segments of the optical fibre link, wherein an initial segment is associated with the receiver and a final segment is associated with the transmitter, wherein each model segment comprises a first linear backpropagation computational model and a nonlinear backpropagation computational model;
• and
• the digital signal processor is configured to:
• receive an input sequence of digital signal samples having a predetermined precision and sampling rate;
• and
• process the input sequence of digital signal samples to compute a distortion-mitigated sequence of output digital signal samples from the input digital samples, said processing comprising, for each one of the plurality of sequential model segments of the optical fibre link proceeding from the initial segment to the final segment:
• 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;
• providing a segment output signal based upon the nonlinear compensated signal;
• and
• 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 comprises the preceding segment output signal, and
• wherein the distortion-mitigated sequence of digital signal samples comprises the segment output signal of the final segment.

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;
• and
• 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;
• computing a second linear compensated signal by processing the nonlinear compensated signal using a second linear backpropagation computational model of the segment;
• providing a segment output signal based upon the second linear compensated signal;
• and
• outputting the distortion-mitigated sequence of output digital signal samples, wherein:
• the first and second linear backpropagation computational models are configured to model respective first and second sub-segments of the segment, the sum of the lengths of said first and second sub-segments being equal to the length of the segment,
• a relative length of each of said first and second sub-segments is determined so as to substantially maximise a degree of mitigation of signal distortion,
• 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.