ABSTRACT
Optical amplifiers are key devices to determine the performance of optical transmission systems. In order to understand the impact of behavior of different amplifiers on the characteristics of optical systems generally it is sufficient good knowledge of the base phenomena that occurs in such devices. All signals cause reflections that propagate through the fiber in the opposite direction of the signal itself. In principle, the theoretical model of an erbium-doped optical fiber amplifier depends critically on the pumping scheme, both due to the possible presence of exited state absorption and to the fact that pumping at 1480 is near to a two-level system. In order to take into account correctly the noise performances of the amplifier, the quantum noise should be taken into account. In a semiclassical picture, this term can be incorporated into the amplifier equations considering the fluxes the average value of a random variable.
