Theoretical and experimental assessment of nonlinearity mitigation through symbol rate optimization

We investigated the reach increase obtained through non-linearity mitigation by means of transmission symbol rate optimization (SRO). We did this first theoretically and simulatively. We show that for PM-QPSK systems at full-C-band the reach increase may be substantial, on the order of 10%-25%, with optimum symbol rates on the order of 2-to-6 GBaud. We extended the investigation to PM-16QAM, where we found a qualitatively similar effect, although the potential reach increase is typically only about half that of PM-QPSK. We then set up an experiment to obtain confirmation of the theoretical and simulative predictions. We demonstrated a reach increase of 11% in a 19-channel, 128Gbit/s per channel, PM-QPSK experiment, when going from single-carrier per channel to multi-subcarrier (up to 16 subcarriers per channel) transmission. The experiment reached 14,100 km over PSCF, with 110 km spans and EDFA-only amplification. The results matched well the model predictions.