Theoretical Analyses of Different Nonlinear Compensation Methods Based on Perturbation Theories in the Unrepeatered System With Raman Amplification

In this paper, the pre- and post-nonlinear compensation (NLC) methods based on regular perturbation (RP) theory are contrastively investigated with the original NLC as a bridge for analyses. Firstly, the numerical error functions of pre-NLC and original NLC are derived, revealing that the numerical error of pre-NLC is more severe due to the error accumulation. Secondly, we deduce the relevance of post-NLC and original NLC, which uncovers the essential difference is that the input condition of post-NLC possesses certain additional information, making the signal's intensity distribution after post-NLC more beneficial for the hard-decision. Meanwhile, the pre-, post- and original NLC methods based on enhanced regular perturbation (ERP) theory have also been discussed. Finally, the simulation is carried out with signal modulation of 16/32/64 QAM and baud-rate of 32 GBaud in an unrepeartered system with Raman amplification. The results agree with the analyses, the post-NLC is the best while the original NLC surpasses the pre-NLC. Additionally, we demonstrate an experiment with signal modulation of 16 QAM and baud-rate of 10 GBaud. The improvements of the Q
²
-factor of the RP-based and ERP-based post-NLC are about 0.6 dB and 1 dB compared with the electronic dispersion compensation (EDC).