Four-Wave Mixing

FWM can be compared to the intermodulation distortion in standard electrical systems. When three wavelengths (λ1, λ 2, and λ 3) interact in a nonlinear medium, they give rise to a fourth wavelength (λ 4), which is formed by the scattering of the three incident photons, producing the fourth photon. This effect is known as four-wave mixing (FWM) and is a fiber-optic characteristic that affects WDM systems.

The effects of FWM are pronounced with decreased channel spacing of wavelengths and at high signal power levels. High chromatic dispersion also increases FWM effects. FWM also causes interchannel cross-talk effects for equally spaced WDM channels. FWM can be mitigated by using uneven channel spacing in WDM systems or nonzero dispersion-shifted fiber (NZDSF). A 0.5-dB power margin is typically reserved to account for the effects of FWM in WDM systems.

August 28, 2011

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