Non-uniform step-size based split step fourier method for mitigating fiber transmission impairments in N-channel 224Gbit/s PolMux-16QAM system

We discuss the performance enhancement of digital backward propagation by step-size selection for implementing split-step Fourier method (SSFM) in 224Gbit/s PolMux-16QAM system. The two DBP algorithms based on the step-size selection methods; (a) constant step-size based modified DBP (M-DBP) and (b) non-uniform, i.e. logarithmic, step-size based DBP (L-DBP), are compared for diverse fiber types i.e. Standard Single Mode Fiber (SMF), Non-Zero Dispersion Shifted Fiber (NZDSF), Large Effective Area Pure-Silica-Core-Fiber (LA-PSCF) and Large Effective Area Fiber (LEAF). Non-uniform step-size distribution enhances the transmission distance upto 32% in large effective area pure-silica-core-fiber (LA-PSCF) link as compared to SMF by employing M-DBP, while we have observed an additional 13% increase in transmission distance by employing L-DBP. Furthermore, the impact of reconfigurable add-drop multiplexers (ROADMs) are also investigated in 10×224Gbit/s system with 50GHz channel spacing grid. ROADMs reduce the signal bandwidth and collectively increase the peak to average power ratio, resulting in higher non-linearities that limits the performance of digital backward propagation. The results also depict that heterogeneous fiber links significantly reduce the nonlinear threshold point (NLT) of the transmission system.