Patent ID: 8611763

Claim:
A method of compensating phase noise in a coherent optical communications network, the method comprising: receiving a traffic sample; receiving an optical carrier and determining a phase noise estimate for the optical carrier by measuring phase variations of the optical carrier and integrating the measured phase variations; the estimate of the phase noise depending on a sampling time, T c , the time interval, t, across which the phase variation is measured, and the measured phase variation; the estimate of the phase noise, {circumflex over (θ)} k , of the optical carrier at a time, k, being determined from θ ^ k = θ ^ k - 1 + T c τ ⁢ z k ′ , where T c is the sampling time, z′ k =z k − z k , z k =∠y k is the phase of the sample y k and z k the average value of z k , {circumflex over (θ)} k−1 is an estimate of the phase noise at an earlier time, k−1, and z′ k is substantially equal to the phase noise variation plus a Gaussian noise contribution added during measurement; and removing the phase noise estimate from the traffic sample to form a phase noise compensated traffic sample.