PHOTON-ECHOES IN AN OPTICAL AMPLIFIER

Accumulated photon-echo experiments in pumped Er-doped fibers are reported. The echoes were observed to decrease and disappear as the fiber was pumped to transparency, and then to increase again as the system was inverted. Coherent saturation between the pulses unbalanced the initially identical excitation pulses. We describe a simple frequency domain model that explains all the observed features.