Decision-Feedback Frequency-Domain Volterra Nonlinear Equalizer for IM/DD OFDM Long-Reach PON

A low-complexity third-order decision-feedback frequency-domain Volterra nonlinear equalizer (DF-FD-VNLE) with superior nonlinearity-compensation performance is proposed and experimentally demonstrated for OFDM long-reach PONs. High optical launch power up to 18 dBm is implemented to mitigate the chromatic dispersion induced power fading and increase the power budget. By reconstructing and subtracting the nonlinear noise in frequency domain with the knowledge of the nonlinear channel, the proposed DF-FD-VNLE outperforms the conventional time-domain VNLE (TD-VNLE) and feed-forward FD-VNLE (FF-FD-VNLE), resulting in better received signal-to-noise ratio (SNR) performance. The nonlinearity-compensation performance of the DF-FD-VNLE can be further improved with the usage of a FF-FD-VNLE or more than one iteration. Complexity and experimental analyses show that similar complexity and higher SNR can be achieved by using the one-iteration DF-FD-VNLE with FD linear equalization (FD-LE), compared with that of the FF-FD-VNLE. Compared with conventional TD-VNLE, the required number of real-valued multiplication (RNRM) of the one-iteration DF-FD-VNLE with FF-FD-VNLE (FD-LE) is reduced by a factor of as much as 82.19% (89.61%) at a memory length of 14 and a truncation factor of 3. Based on the one-iteration DF-FD-VNLE with FF-FD-VNLE, around 53.79 Gb/s single wavelength OFDM IM-DD transmission over 60.8-km SSMF is successfully demonstrated at a BER of 3.8 × 10^-3 and a received optical power (ROP) of -2 dBm, achieving 15% capacity improvement compared to the conventional TD-VNLE.