Precoding and equalization in digital coherent optical transmission

Digital signal processing techniques offers many advantages, such as the simplification of the transmission channel, flexibility of transceivers, and efficient compensation of almost any transmission impairment. Digital signal processors have been recently introduced in coherent long-haul optical transmission systems, as well as in non-coherent access networks. In this contribution, we review a number of specific signal processing algorithms that are useful in such systems. We focus on advanced equalizers for linear and nonlinear distortions. We examine the Tomlinson-Harashima precoding approach, as well as advanced flexible non-integer fractionally-spaced equalizers in a butterfly structure. For the compensation of fiber nonlinearities, Volterra based equalization is investigated.