Design optimization of hybrid erbium-doped fiber amplifiers for WDM transmission systems

For realizing wavelength-division multiplexing (WDM) transmission systems, one of the most important devices is the erbium-doped fiber amplifier (EDFA), which exhibits a flat gain, a high pumping efficiency, and a low noise figure (NF). To meet these requirements, we have optimized the hybrid EDF configurations composed of cascaded Al codoped EDF and P/Al codoped EDF. Their characteristics have been theoretically and experimentally examined, and it has been shown that the hybrid EDF is superior in terms of both the gain flatness and the pumping efficiency, but the NF tends to be worse than conventional EDF configurations. Thus a midway isolator should be inserted. As a result of the design optimization, three-section hybrid EDE configurations have been proposed, and two types of EDFAs have been developed for use as in-line amplifiers and preamplifiers. Both types exhibit a passband spanning about 15 nm. In experiments employing a five-cascaded in-line amplifier chain, a total gain deviation of less than 2 dB has been demonstrated, while the total loss budget is about 125 dB. (C) 1997 Academic Press.