Abstract

Distributed erbium-doped fiber amplifiers (EDFAs) have been in the literature recently. Since the length of a distributed EDFA can be several tens of kilometers, the losses of the signal and pump power along the EDFA must be considered. It is known that for such cases backward pumping gives higher gain than does for-ward pumping, but the noise figure is also higher.⁹ Hence, there must exist some optimal forward to backward pump power ratio that yields the best overall performance for a bidirectionally pumped EDFA. An analysis of bidirectionally pumped EDFAs for small-signal level was given in Ref. 2, concentrating on closed-form expressions and the optimal Er³⁺ absorption coefficient. In this paper, we analyze the bidirectionally pumped EDFA by numerically solving the differential equations of forward and backward pumps, forward and backward amplified spontaneous emission, and the signal. We show how the gain, amplified spontaneous emission, and noise figure of such an EDFA change with signal level and the ratio of backward to total pump power. The results of this analysis provide a basis for optimizing EDFA performance.

© 1992 Optical Society of America