Design and modelling of saturated erbium-doped fiber amplifiers

Erbium doped fiber amplifiers operating in signal saturated regime have become the key components of the rapidly growing WDM and cable TV optical communication systems. Therefore efficient design and accurate modeling of gain and NF in saturated EDFAs is of prime importance. It is generally believed that for achieving efficient EDFAs, the erbium doping inside the fiber should be confined, Although this is true for amplifiers operating in small signal regime, we show that for the case of saturated EDFAs optimum design is achieved when erbium is not confined and distributed over the entire fiber core. Another issue is the modeling of these non-confined EDFAs. The existing steady state EDFA models can be categorized into two major groups. First are the so-called general models which include the radial optical and erbium distributions: however these models are not very practical as they include many parameters some of which are difficult to measure accurately. Second are the simplified models of Giles [1991] and Saleh [1991] which are based on the effective overlap integral and provide a more practical way in modeling EDFAs; however, both of the models are derived based on the assumption that the erbium is confined inside the fiber core and as a result cannot accurately predict the performance of nonconfined EDFAs. In this paper we present a model which can closely predict the gain and NF of saturated EDFAs irrespective of the erbium confinement.