Rayleigh scattering effect on the gain efficiency and noise of erbium-doped fiber amplifiers

The effect of the internal Rayleigh scattering on the gain efficiency and noise of the erbium-doped fiber amplifier has been considered in detail. It is shown that excess background loss due to Rayleigh scattering at the signal and pump wavelengths dramatically reduces the optimum gain efficiency of either high NA, low-concentration or confined-dopant erbium-doped fibers. Distributed feedback due to Rayleigh backscattering, on the other hand, degrades the noise performance of high gain amplifiers considerably. In applications where high gain and low noise figure are required, increasing the fiber NA and dopant confinement above an optimum value are shown to increase the required pump power dramatically due to the deleterious effects of Rayleigh backscattering