Fiber amplifier technology is in the fiber core of the doped can produce laser rare earth elements, through the laser to provide DC excitation, so that through the optical signal to be amplified. The traditional optical fiber transmission system is the use of optical electrical optical regenerative repeater, the relay equipment affect the system's stability and reliability, to get rid of the conversion process directly in light path to amplify the signal transmission, instead of the regenerative repeater with an all-optical transmission repeater. For the equipment of erbium doped fiber amplifier (EDFA), praseodymium doped fiber amplifier (PDFA) and Nb doped fiber amplifier (NDFA). At present, the optical amplification technology is mainly used EDFA.