Qualitative comparison of Kerr nonlinearity mitigation schemes in a dispersion-managed link for 4 × 28-GBd 16-QAM signals

We present an experimental investigation of different Kerr nonlinearity mitigation schemes in a 2-span dispersion-compensated link of 160-km length for 4 × 28-GBd single-polarization 16-QAM signal transmission. We consider optical phase conjugation (OPC) based on mid-link spectral inversion, digital backpropagation (DBP), and transmission of phase-conjugated twin-waves with either digital coherent superposition (DCS) or all-optical coherent superposition employing phase-sensitive amplification (PSA). The experiments are performed in a single-channel and a wavelength-division multiplexing (WDM) scenario. For single-channel operation, phase-conjugated twin waves with DCS provided superior performance compared to all the other mitigation schemes with a maximum Q2-factor improvement of 1.7 dB compared to signal transmission without any nonlinearity mitigation. The DBP, however, showed a higher nonlinear threshold than all the other schemes in our experiments. In the WDM scenario, DBP showed worse performance than the other mitigation schemes whereas the DCS again provided a higher Q2-factor improvement than the other techniques with a maximum Q2-factor improvement of 1.9 dB. The PSA and the mid-link OPC showed similar nonlinearity mitigation performance both in single-channel and WDM scenarios.