Abstract

Various optical and electrical feedback automatic-gain-control (AGC) technologies have been developed in order to achieve constant gain in erbium-doped-fiber-amplifiers (EDFA). Commercially, however, to the best of authors’ knowledge, only electrical feedback AGC is used due to the complexity and the cost penalty of the other technologies. The electrical AGC feedback circuit adjusts the EDFA pump power according to the difference between the measured gain and the required gain. However, in the case of fast channel dropping, e.g. due to fiber-cut, the feedback-controlled EDFA generates huge power surge. This power surge causes higher bit-error-rate and may eventually damage the receiver as it grows in the downstream EDFAs. The origin for the power surge is the effective lifetime (~100 μs) of erbium states, which makes it difficult to realize fast feedback loop. Here we present a practical and low cost EDFA control solution in which both electrical feedforward and feedback are employed. We have demonstrated that with this AGC technology the gain excursion happening in WDM systems can be drastically reduced.

© 2002 Optical Society of America