Design of gain-clamped doped-fiber amplifiers for optimal dynamic performance

This paper provides a detailed analysis of gain-clamped doped-fiber amplifi ers and design guidelines in a wavelength division multiplexed (WDM) networ king environment, A simple dynamic model of the doped-fiber amplifier allow s us to derive explicit expressions for the small-signal response, which he lp identify and optimize the most critical parameters for best dynamic perf ormance. The most important parameter is the pump power, which should be ch osen 1-2 dB's above its required open-loop value, with all channels present , for the required signal gain. In an all-optical networking scenario with input power per channel as high as -3 dBm the required pump power mag well exceed 20 dBm, Thus optimization of other parameters such as laser waveleng th and loop loss are important. For best dynamic performance either the loo p loss should be extremely small, implying a very large laser Bur, or the l aser gain variation in response to a perturbation should be large. Accordin gly, the laser wavelength should be placed either close to the unity-gain r egion of the clamped gain profile, or at its peak. Finally, the small signa l model for a chain of clamped amplifiers is provided, and it is shown that long chains are vulnerable to low-frequency input signal perturbations.