Performance Degradation due to Four-wave Mixing in Multichannel Coherent Optical Communications Systems

Bit-error rate (BER) degradation due to four-wave mixing (FWM), in multichannel coherent optical communications systems, is studied. In particular, analytic expressions for the BER are derived for ASK, PSK, and FSK modulation schemes. The effects of input power, fiber chromatic dispersion, number of channels, and inter-channel spacing on the BER degradation is explicitly shown. The results show that, on the basis of equal peak power per channel, the ASK noncoherent detection scheme has the best performance, while the PSK coherent detection scheme has the poorest performance. For 1.55 μηι 100 channels transmission systems, having 5 GHz inter-channel spacing, the analysis predicts a maximum allowable input power per channel to be 2 dBm for 100 km of conventional single-mode fibers, and only — 9 dBm for 100 km of dispersion-shifted fibers. Finally, these analytical results are found to be in good agreement with recent experimental results.