Optical post amplifiers, used to increase the strength of the signal generated by the optical transmitter often use a diode-pumped erbium-doped fiber laser. The diode is often a high power 980 or 1480 nm laser diode. This setup allows for an amplification of up to +24dBm in an affordable manner. Using an erbium-ytterbium doped fiber instead allows for a gain of +33dBm, however again the amount of power that can be fed into the fiber is limited. In single carrier configurations the dominating limitation is self phase modulation induced by the Kerr effect which limits the amplification to +18 dBm per fiber. In WDM configurations the limitation due to crossphase modulation becomes predominant instead. Optical pre-amplifiers are often used to negate the thermal noise of the receiver. Pumping the pre-amplifier with a 980 nm laser leads to a noise of at most 3.5 dB, with a noise of 5 dB usually obtained with a 1480 nm laser. The noise has to be filtered using optical filters.
oPticaL poSt ampliFiERs, useD To iNCreAsE thE Strength Of tHe signal geNerated BY THE OptIcaL TRansmitter oFTeN USE a dioDE-puMpED erbiUm-doPed fibeR laSer. the dioDe Is often a hiGh POWer 980 or 1480 Nm lASeR diODE. this SEtup ALLows foR An amPliFicatIoN of Up To +24dbM In aN AfFOrDaBle manner. uSing an erbiUm-yTTerbiuM doped fiber InsteAd AllOws fOr A gain of +33Dbm, however agAin The aMoUnT of power that can bE fed InTO thE fiBer is lIMiTEd. In SIngLe carrieR ConfiGuRaTiOns THe DominatIng LImitAtIoN is SELf PhasE mOdulation inDuced By thE kerr effecT whiCh limITS tHE AmPlIficatiOn To +18 DBm Per FIbEr. iN WDm COnfiguRaTIoNS The LIMItAtiOn due to CROsSPhAse modULatioN BEComes PredOmINaNt InstEad. OPtIcAL PRe-aMpLiFiErS are ofteN used to negAte the tHerMAl noise Of the ReCeiVer. pUmpIng The PrE-amplIFieR With a 980 NM laseR leAds tO a NOIse of At MOSt 3.5 Db, witH a Noise Of 5 db uSUAlly ObtaineD with A 1480 Nm laSeR. tHe NoisE has to Be FiLTerEd UsiNg optical fIlters.