Enhanced Compensation of Nonlinear Signal Distortion by Optical Phase Conjugation in Step-Parameter Profiled Fiber Links

Improving the efficacy of optical phase conjugation (OPC) for compensating nonlinear signal distortion in long distance optical fiber links from the Kerr effect is demonstrated. This is based on tailoring the link spans as step-parameter profiled fiber (SPF) for progressively increasing nonlinearity and decreasing dispersion with distance to mitigate the impact of propagation loss on unbalancing the phase distortion induced before and after OPC. With addition of a dispersion element after OPC, the SPF design also targets compensation in a shorter subsection of spans where induced nonlinear distortion is strongest. This enables performance benefit with less required parameter change in spans comprising just two or three segments of different regular fibers as 2-SPF and 3-SPF, respectively. Numerical simulations of 5 channel WDM dual polarization (DP) 32 Gbaud 64-QAM signals in a 12 × 130 km fiber link shows use of OPC and a 58 km 3-SPF in spans achieves 2.1 dB higher Q² -factor at 5 dB higher launch power than without. Similarly, measurements of 5 channel WDM DP 12 Gbaud 16-QAM signals in a 2 × 155 km link shows use of OPC and a 41 km 2-SPF in spans achieves 1.2 dB higher Q² -factor at 6 dB higher launch power and with low bit error rate compared to without. The improvements highlight the OPC advancements achievable by link design with regular fibers.