Compensation of Nonlinearity Impairments in Coherent Optical OFDM Systems Using Multiple Optical Phase Conjugate Modules

In this paper, we propose utilizing multiple optical phase conjugate (OPC) modules along fiber spans, in order to improve the performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) communication systems in long-haul fiber-optic channels. The role of OPC in CO-OFDM systems is investigated by formulating the four-wave mixing (FWM) process generated along a CO-OFDM with two and three OPCs. Analytical results reveal that increasing the number of OPC modules reduces the average FWM power along the transmission link and as a result mitigates the degrading effect of interaction between amplified spontaneous emission noise and FWM. The proposed schemes have also been investigated using numerical simulations. The results indicate that increasing the number of OPC modules improves the bit error rate (BER) performance and enlarges the transmission reach of CO-OFDM systems. In the case of using three OPC modules, compared to utilizing only one, the BER performance is enhanced nearly two orders of magnitude, and the transmission reach of the system increases in dispersion-unmanaged and dispersion-managed scenarios by 52% and 37%, respectively.