Method and system to identify and characterize nonlinearities in optical communications channels

A method for enhancing the behavior of an optical fiber data channel the method comprising:

• determining a sequence of data input to the optical fiber data channel;
• determining a Volterra Series representation of the channel;
• accepting at least part of the sequence of data input to the data channel into the Volterra series representation of the channel to produce a channel model value;
• sampling the data after it has passed through the channel to produce a sampled value;
• comparing the channel model value with the sampled value;
• adjusting the channel model value based on the results of the comparison between the channel model value with the sampled value;
• identifying non-linearities in the optical fiber data channel based on the adjusted channel model;
• and
• compensating for the non-linearities to enhance channel performance.

A method for equalizing an optical signal, modulated with a digital signal, received over an optical channel, the method comprising:

• converting the optical signal into an electrical signal;
• summing the electrical signal with a correction signal;
• providing the summed signal to a detector;
• detecting the summed signal to produce decisions;
• providing the decisions to a nonlinear channel estimator;
• estimating the correction signal in the nonlinear channel estimator;
• and
• adapting the estimating in the nonlinear channel estimator in accordance with the decisions.

An apparatus for equalizing a signal received over an optical channel, the apparatus comprising:

• an input that accepts an optical signal;
• a converter that converts the optical signal into an electrical signal;
• a summation unit that sums the electrical signal with a correction signal;
• a detector that detects the summed signal to produce decisions;
• and
• a nonlinear channel estimator that estimates the correction signal and adapts the estimating in accordance with the decisions.

A method for decoding a signal received over an optical channel, the method comprising:

• receiving a signal including linear and nonlinear components;
• estimating, in a nonlinear channel estimator having a memory width, expected values of the received signal;
• computing branch metrics over a number of states based on the expected values of the received signal, wherein the number of states corresponds to the memory width;
• providing the computed branch metrics to a Viterbi decoder;
• and
• Viterbi decoding the received signal using the branch metrics provided to the Viterbi decoder.

An apparatus for decoding a signal received over an optical channel, the apparatus comprising:

• a receiver for receiving a signal including linear and nonlinear components;
• a nonlinear channel estimator, having a memory width, that computes expected values of the received signal;
• a branch metrics computer for computing branch metrics over a number of states based on the expected values of the received signal, wherein the number of states corresponds to the memory width;
• a Viterbi decoder that accepts the computed branch metrics and Viterbi decodes the received signal.

A method for detecting digital data modulated on an optical signal and received over an optical channel, the method comprising:

• converting the optical signal to an electrical signal;
• converting the electrical signal to a multibit digital representation;
• estimating distortion introduced in the optical signal by the optical channel;
• compensating the multibit digital representation for the distortion;
• and detecting the digital data from the compensated multibit digital representation.

An apparatus for detecting digital data modulated on an optical signal and received over an optical channel, the apparatus comprising:

• a converter for converting the optical signal to an electrical signal;
• an analog to digital converter that converts the electrical signal to a multibit digital representation;
• an estimator that estimates distortion introduced in the optical signal by the optical channel;
• a compensator that compensates the multibit digital representation for the distortion;
• and a detector that detects the digital data from the compensated multibit digital representation.