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One of the most promising technologies in optical networks is the use of wavelength-division multiplexing (WDM), in which many different-wavelength channels are simultaneously transmitted along the optical fiber. One key underlying technology which has enabled these systems is the introduction of the erbium-doped fiber amplifier EDFA. A glaring disadvantage of the EDFA is that the gain is not uniform with wavelength, causing a significant power and signal-to-noise ratio (SNR) differential among many channels. We will discuss our demonstrations of dynamically equalizing three 2.5 Gbit/s WDM channels in which the channel power differential is reduced from 20 dB to only 1 dB over a distance of 2,500 km by placing an acousto optical filter in an EDFA.