Gain in erbium-doped fiber amplifiers: a simple analytical solution for the rate equations.

The solution of the rate equations that describe an erbium-doped fiber amplifier is investigated, and the possibility of obtaining an analytical solution for several field and erbium transverse distributions in the active fiber is determined. With the obtained equations it is possible to find directly the signal gain and the main parameters that influence it. The validity of this research is extended to the case of high signal power.