Multi-span digital non-linear compensation for dual-polarization quadrature phase shift keying long-haul communication systems

We have numerically investigated a method to reduce the complexity of the digital backward propagation algorithm (DBP). A filtered logarithmic step-size based split-step Fourier method (SSFM) is investigated in this paper to digitally compensate chromatic dispersion (CD) and non-linearities (NL) in dual-polarization quadrature phase shift keying (DP-QPSK) systems. The algorithm was evaluated for coherently-detected multiple channel DP-QPSK system over un-compensated transmission links with diverse baud-rates i.e. 14 GBaud, 28 GBaud and 56 GBaud. The results depict efficient mitigation of CD and NL, therefore improving the non-linear threshold point (NLT) by 4 dB. Furthermore by implementing a low-pass-filter (LPF) in each DBP stage, the required number of DBP stages are significantly reduced (multi-span DBP) by 75%. The results delineate improved system performance of logarithmic step size based filtered DBP (FL-DBP) both in terms of efficiency and complexity which will be helpful in future deployment of DBP algorithm with real-time signal processing modules for non-linear compensation.