A theoretical investigation of dynamic all-optical automatic gain control in multichannel EDFA's and EDFA cascades

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We present a detailed theoretical analysis of the gain dynamics of erbium-doped fiber amplifiers (EDFA's) that have been gain-clamped using a ring laser structure and of gain-stabilized EDFA chains. We examine and analyze the effects of attenuator level in the optical feedback path, switching speed, number of channels dropped or added and the choice of lasing wavelength on the stabilization of the individual EDFA. In particular, we look at the transient power excursions and relaxation oscillations experienced by surviving channels when the number of channels passing through an EDFA changes. Using this analysis as a guide, we present and compare two different approaches to chain stabilization. We highlight the robustness of each approach, show some of their limitations and advantages, and comment on the impact on multiwavelength communication systems.