A new configuration for erbium-doped fiber lasers in which two differe
nt connected fibers are used is studied: one is heavily and the other
weakly doped. It is demonstrated that the dynamics of such a system de
pends on the fiber into which the pump is injected. The experimental r
esults are interpreted in the framework of an ion-pair interaction mod
el. (C) 1996 Optical Society of America