Optoelectronic regenerators have been used in traditional opticai communication systems to convert signals from the optical to electrical and then back to the optical domain. Since its first report in 1987 11,21, the erbium-doped fiber amplifier (EDFA) has revolutionized optical communications. This optical amplifier does not need high-speed electronic circuitry and is transparent to data rate and format, which dramatically reduces cost. EDFAS also provide high gain, high power, and low noise figure. More importantly, all the optical signal channels can be amplified simultaneously within the EDFA in one fiber, thus enabling wavelength-thvision-mWtiplexing (WDM) technology. Due to the recent exponential growth in data communication and the Internet, there is an urgent demand on high capacity communication networks. To increase the total capacity, one can work on one or both of the two things, 1) high speed, which is currently limited by high speed electronics and fiber dispersion and nonlinear effects, and 2) large numbers of channels which is in turn determined by the available bandwidth and channel spacing. Since signal channel spacing is limited by filtering technology, modulation speed and format and nonlinear effects, much attention has been paid to increasing the optical amplifier bandwidth in the recent years.