The statistical characterization of the nonlinear noise in Tbps Densely Spaced PDM CO-OFDM Systems under different modulation formats

The statistical characterization of the nonlinear interference (NLI) within Tbps coherent optical OFDM (CO-OFDM) systems is studied by simulation under the circumstance of uncompensated transmission, encompassing three different kinds of modulation formats, such as PDM-QPSK and PDM-mQAM (m=16, 64). The simulation results show that the statistical distribution of NLI is Gaussian distributed in PDM-QPSK CO-OFDM systems. Nevertheless, the NLI distribution deviates from Gaussian in PDM-mQAM CO-OFDM systems, due to its multi-level envelop of symbols and high peak to average power ratio (PAPR). We also observe that the variance of the NLI depends on the launch power and the transmission distance in a linear way.