Statistics of Four-Wave Mixing Crosstalk

Four-wave mixing (FWM) is the dominant nonlinear effect in intensity-modulated wavelength-division multiplexed (WDM) optical communication systems using dispersion-shifted fiber (DSF). In WDM systems with equally spaced channels all the product terms generated by FWM in the bandwidth of the system fall at the channel frequencies. The mixing products generated at the channel frequencies coherently interfere with the signals, giving rise to crosstalk. Due to the coherent nature of FWM interference in equally spaced WDM systems, a single mixing product generated on one of the channels with a power 20 dB lower than the signal power is enough to cause a ±1 dB fluctuation in the received power [1].