Transmission performance of high baud superchannels in optical fiber communications

In high baud fiber-optic communication systems, the bandwidth limitation at the transmitter and receiver, and the linear and nonlinear responses of electro-optical components, drive amplifiers and digital-to-analog converters can introduce pattern dependent distortion that caused the signal-quality degradation. Furthermore, the use of narrow subcarrier spacing leads to cross-phase modulation (XPM) distortion considered one of the main obstacles to achieving large transmission distances in superchannel systems. The primary objective of this research is to mitigate the effect of pattern dependent distortion and enhance the transmission performance of high baud superchannel systems.;Transmission of single-subcarrier 448 Gb/s dual-polarization 16-ary quadrature-amplitude modulation (DP 16-QAM) signal and a 1.206 Tb/s three-subcarrier superchannel signal using DP 16-QAM is demonstrated by applying a fixed look-up table (LUT) based on maximum-a-posteriori probability (MAP) detector at the receiver. Different decision rules for the MAP detector are considered based on multiple observations of the same symbol as the detection window advances through the received symbol sequence. Alternative approaches include a LUT based nonlinear pre-distorter (NLPD) at the transmitter, and a Volterra nonlinear equalizer (VNLE) or sparse-VNLE at the receiver. The LUT based NLPD with iterative calculation of the pre-distortion provides the best performance in back-to-back systems and transmission systems followed by the MAP detector, VNLE and sparse-VNLE.;For a 1.206 Tb/s DP 16-QAM Nyquist-superchannel using 3, 5 and 9 subcarriers, the impact of the number of subcarriers on the relative strength of the intra- and inter-subcarrier nonlinearities and on the maximum achievable transmission distance for an information rate of 1 Tb/s is determined by simulation. The degree of correlation for the inter-subcarrier nonlinearity induced phase perturbation is assessed between a modulated center subcarrier and a continuous wave (CW) probe center subcarrier. The results provide an indication of the reliability of statistical information about the nonlinear phase perturbation that can be obtained from a probe signal either through simulation or experiment.