Abstract
Erbium-doped fiber amplifier (EDFA) featuring a spectrally flattened gain is considered to be one of the most important key devices for the wavelength-division multiplexing (WDM) transmission systems. For this purpose, we have developed hybrid EDFs composed of Al doped EDF and P/Al co-doped EDF and examined their characteristics comparing with the conventional EDFs and those with passive gain equalizers. As a result, hybrid EDFs have been shown to exhibit both a flat gain and high pumping efficiency, but their noise characteristics 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 EDF configuration has been proposed, and three types of EDFAs have been developed employing this configuration for use as in-line amplifiers or preamplifiers. All types exhibit the passband spanning about 15nm.
