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Nonlinearity-induced phase noise has become a major obstacle in long-haul coherent fiber-optic communication systems. Such phase noise has been shown to be signal dependent, and correlated over time. We propose a code-aided expectationmaximization algorithm to mitigate such nonlinear phase noise, iteratively utilizing both the time correlation of the nonlinearityinduced impairments and a soft-decision error-control code. Simulation and experimental results show that on a dual-polarization wavelength-division-multiplexed 16 QAM system, launch-power tolerance can be increased by 1.5 dB, and the optical signal-tonoise ratio requirement can be relaxed by 0.3 dB to achieve the same Q 2 -factor.

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An adaptive LLR calculation algorithm is proposed for non-additive-white-Gaussian-noise (non-AWGN) optical channels. The noise distribution is continuously up-dated based on previous decisions. The performance is tested experimentally using 16-QAM and soft-DQPSK systems.

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