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 information defining a backpropagation model of the optical fibre link, said backpropagation model comprising one or more sequential segments of the fibre link, wherein an initial segment is associated with the receiver and a final segment is associated with the transmitter, wherein each segment is modelled as at least a first linear backpropagation element and a non-linear backpropagation element having an associated compensation bandwidth;
• and
• the digital signal processor is configured to receive a sequence of input digital samples having a predetermined precision and sampling rate, and to generate a distortion-mitigated sequence of output digital samples from the input digital samples by computing, for each sequential segment in turn, a first linear compensated signal from a signal input to the segment in accordance with the first linear backpropagation element, and a non-linear compensated signal from the first linear compensated signal in accordance with the non-linear backpropagation element, wherein computation of the non-linear compensation signal comprises limiting a bandwidth of a compensation signal derived from the first linear compensated signal in accordance with the associated compensation bandwidth.

A method for equalisation of a signal to mitigate distortions of the signal in traversing an optical fibre link from an optical transmitter to a corresponding optical receiver, the method comprising:

• providing a computational backpropagation model of the optical fibre link, said model comprising one or more sequential segments of the fibre link, wherein an initial segment is associated with the receiver and a final segment is associated with the transmitter, wherein each segment is modelled as at least a first linear backpropagation element, a non-linear backpropagation element, and a second linear backpropagation element;
• applying the computational backpropagation model to the signal to generate a distortion-mitigated signal by computing, for each sequential segment in turn, a first linear compensated signal from a signal input to the segment in accordance with the first linear backpropagation element, a non-linear compensated signal from the first linear compensated signal in accordance with the non-linear backpropagation element, and a second linear compensated signal from the non-linear compensated signal in accordance with the second linear back propagation element;
• and
• outputting the distortion mitigated signal,
• wherein the first and second linear backpropagation elements correspond with first and second continuous sub-segments of the associated segment of the fibre link, the sum of the lengths of said first and second sub-segments being equal to the length of the associated segment, and the relative length of each of said first and second sub-segment being determined so as to substantially maximise a degree of mitigation of signal distortion.