I. Introduction
The exploding demand for Internet access and broadband services has led to the push for greater lightwave transmission capacity. Wavelength-division-multiplexing (WDM) systems can accommodate the increase in this demand by increasing the number of signal wavelengths propagating on a single fiber. These systems will evolve from point-to-point transmissions to next-generation WDM systems that are incorporated with reconfigurable add/drop nodes. Optical signal power levels in such systems are generally different for every wavelength because of the intrinsically nonflat gain profiles of erbium-doped fiber amplifiers (EDFAs) and the dependence of optical signal levels on network configuration. Since this difference in power levels degrades the signal-to-noise ratio, it is important to keep the levels constant over all channels. Consequently, a dynamic gain equalizer (DGE) is required to automatically compensate for variations in optical signal power levels.