NSNI Mitigation in Bi-Directional Raman Amplified Unrepeatered System Using Split-DBP

The nonlinear signal-noise interaction (NSNI) is analyzed in the bi-directional Raman amplified unrepeatered system with digital back-propagation (DBP) algorithm. When the DBP is applied at the receiver side, because in the DBP process the spontaneous Raman scattering is not dealt with, extra NSNI occurs, and because of the high power in the system, the extra NSNI is severe. By adopting split-DBP, the interaction of noise and signal in the high-power region could be avoided. Thus, the extra NSNI was mitigated and the performance was improved. The performance of split-DBP algorithm in such a system was investigated through simulations and experiments, using a single-channel 300-km bi-directional Raman amplified unrepeatered system. The simulations were carried out with 16 QAM modulation and the modulation rates were 32 GBd and 10 GBd. The results showed that the split-DBP can deliver 0.8-dB Q
²
-factor improvement for the case of 32 GBd and 1.3 dB for the case of 10 GBd, compared to the traditional DBP. The impact of the nonlinear transform function of modulator and power profile mismatch on the performance of split-DBP is discussed through the simulation, which is critical to the practical implementation of split-DBP. An experimental demonstration of the split-DBP with 10 GBd 16 QAM modulation was carried out. The experimental results presented a 1.2-dB Q
²
-factor improvement of the signal due to split-DBP.