Enabling Technologies for Fiber Nonlinearity Mitigation in High Capacity Transmission Systems

Fiber nonlinearity has become a major limiting transmission impairment factor. In this paper, we discuss various nonlinearity mitigation techniques in electrical and optical domains. In electrical domain, multiple reduced complexity digital back-propagation algorithms were developed, including perturbation back-propagation. One drawback is that they can compensate for intra-channel self-phase modulation (SPM) effects only. The inter-channel fiber nonlinearity mitigation can be done in optical domain. For example, digital subcarrier multiplexing (SCM) can effectively mitigate both SPM and cross-phase modulation (XPM) effects. It can become even more beneficial for higher symbol rate systems (e.g., 64 Gbaud and 128 Gbaud) and has a capability to deliver longer reach than single carrier 32 Gbaud DP-16QAM signals and only slightly shorter reach (by up to 7%) compared to 32 Gbaud SCM systems. Another technique, the total intensity directed phase modulation, can provide per-span SPM and XPM compensation. However, this technique is limited to compensation of a few channels only. On the other hand, the proposed enhanced pre-dispersed spectral inversion can effectively compensate for SPM/XPM effects of multiple channels and become more practical by removing limitation to link symmetry even in nonuniform transmission links. Finally, subcarrier power pre-emphasis in optical superchannels can equalize performance of all subcarriers by mitigating intersubcarrier XPM and extend transmission reach by 20%.