Longhaulwavelengthdivisionmultiplexing(WDM)hastransformedthetransmissiontechnologyandalso theeconomicsofopticalnetwork,andthereisnoelec tronicsregenerationinthesystemsoastobreakthelimitofthe“electronicsbottleneck”.Inordertoimprove thetransmissionperformanceandprolongtheerror free transmitteddistancewithoutelectronicrelay,muchwork havebeendonetodevelopthistechnologywhichcanbesummarizedintwofollowingways.Firstbymeansof powercontrol,somesystemsuseErbium DopedFiber Amplifier(EDFA)[1]orFiber…