Digital equalization of optical nonlinearities in very high-speed optical communication systems

We review recently proposed nonlinear mitigation methods based on a frequency-domain Volterra series expansion for high-speed and long-haul optical transmission systems. Using a symmetric kernel reconstruction we derive a set of parallel frequency-domain filters that constructively add up to rebuild the matrix-based Volterra series nonlinear equalizer (VSNE). It is demonstrated through simulation results that a reduced set of symmetric VSNE (symVSNE) filters is able to achieve a near-optimum performance. In addition, a constant-coefficient approximation is used to obtain a simplified VSNE (simVSNE), achieving several orders of magnitude computational gain. The validity of this approximation is shown to mostly depend on the amount of accumulated chromatic dispersion to be compensated per simVSNE iteration, therefore impacting the spatial resolution requirements of the algorithm.