Rapid calculation of nonlinear optical transmission impairments

A method of estimating impairments of an Optical Channel (OCh) trail between a transmitter and a receiver in an optical communications network, the method comprising:

• computing a respective per-span nonlinear field variance for each span of the OCh trail, the per-span nonlinear field variance representing nonlinearly induced noise due to the transmission impairments of the respective span, the nonlinearly induced noise being imparted to a signal transmitted through the OCh trail and detected by the receiver;
• computing a respective covariance between the nonlinear fields contributed by each span pair of the OCh trail, the covariance representing the correlation of the nonlinearly induced noise imparted to the signal within the first span of a span pair with the nonlinearly induced noise imparted to the signal within the second span of the pair;
• populating a covariance matrix using the computed per-span variance values and covariance values;
• and
• computing a total nonlinear field variance by summing over the covariance matrix elements.