SPM compensation for long-haul CO-OFDM systems with midlink optical phase conjugation

Midlink optical phase conjugation (M-OPC) based on four wave mixing (FWM) in semiconductor optical amplifier (SOA) can be used to compensate for the fiber nonlinearity effect in CO-OFDM systems. Simulation of 40 Gb/s CO-OFDM systems without optical dispersion compensation is presented. For a single-channel system, even greater benefits are obtained and the nonlinear limits are significantly decreased: the maximum Q can be increased by 3 dB for all transmission distances greater than 2400 km, the nonlinear threshold (NLT) (for Q > 10 dB) is increased by >4 dB. Due to cross phase modulation (XPM) from neighbouring WDM channels, the maximum Q and NLT are increased by about 1.1 dB and 1 dB for 50-GHz-spacing WDM systems separately. These results show that M-OPC can mitigate the fiber nonlinearity impairment for both single-channel and WDM systems.