Typicalspacing rangespaceAs we have seen earlierwhen the attenuation problem was solvedattenuationdispersion effects became significanteffectssignificantSimilarlynon-linear effects in fiber became dominantThe nonlinear effects—stimulated Raman scatteringstimulated Brillouin scatteringself-and cross - phase modulationandfour-wavemixing—maypotentially limit the performancemaximum transmission rateStimulatedStimulated Raman scattering is caused by theinteraction of theoptical signal with silica molecules in the fiberThis interaction can lead to transfer of power from lower-wavelength channels to higher-wavelength channelsinteractionoptical signal and acoustic waves in the fiberinteractiontoward the transmit-terthe index of refraction depends on the optical intensity of signals propagating through the fiberSelf-phasevariationsresultsSelf-phase modulation is caused by variations in the power of an optical signal and results in variations in the phase of the signalphase shifts get transformed to signal distortionBy contrastintensitysignal propagating at a different wavelengthwhich can cause interference if they overlap with frequencies used for data transmissionThe above nonlinearities in fiber can be controlled by careful choice of channel power and channel spacing.The advent of EDFA enabled commercial development of WDM systems by providing a way to amplify all the wavelengths at the same time
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