One of the key advantages of erbium-doped fiber amplifiers (EDFAs) is their immunity to crosstalk, because of their inherently slow (100-μs–1-ms) gain dynamics.1 This lack of crosstalk makes EDFAs suitable for use in multichannel fiber networks. In such applications, however, occasional bursts of traffic may result in gain fluctuations because of transient saturation in the EDFA, causing packet-to-packet data interferences. Automatic gain control (AGC) loops can be used to achieve such necessary gain stabilization. A feed-forward AGC loop was shown;1 it acts on the pump source to increase the gain as a transient of higher signal power as detected at the EDFA input. The main disadvantage of AGC through pump power control is the large pump power change, ΔPp, necessary to compensate for the gain fluctuation, ΔG (e.g., ΔPp ≈ 15 mW for ΔG ~ 3 dB).2 In this paper we demonstrate an alternate scheme for AGC feedback loops requiring a comparatively very lowcontrol power of 2 μW. In this scheme, the error signal is generated by the fluctuations of output amplified spontaneous emission (ASE). This signal is applied to modulate the intensity of a control or compensation signal input to the EDFA to maintain a constant level of gain saturation in the amplifier.

© 1991 Optical Society of America

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