Improved nonlinear tolerance in ultra-dense WDM OFDM systems

This paper demonstrates and experimentally validates the Zadoff–Chu matrix transform (ZCT) precoding as a peak-to-average power ratio (PAPR) reduction technique for coherent optical orthogonal frequency division multiplexing (OFDM) over ultra-dense wavelength division multiplexing (UDWDM). The work provides performance comparison between conventional and the precoded UDWDM–OFDM system. The system use case was implemented by 16-QAM–OFDM modulated channels among 3.5 GHz, 7 GHz, and 10 GHz channel spacings scenarios. The ZCT precoding approach improves the nonlinear tolerance in UDWDM–PON systems. The performance in terms of error vector magnitude (EVM) and bit error rate (BER) is presented after transmission over 40 km of standard single mode fiber (SSMF). The results show a significant EVM improvement considering the aforementioned channel spacings and for different number of UDWDM channel groups in the nonlinear regime operation. The implemented ZCT precoding system outperforms the non precoded approaches in terms of EVM and BER results.