Digital non-linear compensation for high-speed long-haul transmission

Thanks to coherent detection and digital signal processing (DSP), linear distortions such as chromatic dispersion (CD) and polarisation mode dispersion (PMD) can in principle be completely compensated for in high-speed optical transmission. And indeed, effective algorithms have been devised and extensively investigated that allow CD- and PMD-resilient transmission of high-speed signals over long distances, leaving optical noise accumulation and non-linear impairments as the factors ultimately limiting reach. Considerable research has been dedicated in the last couple of years so devise methods to increase the non-linear tolerance of optical signals by means of digital signal processing. In this paper, we present an overview of the most promising techniques, show some examples of their application and outline the status of research on this important topic.