Application of the all-optical gain-controlled (AOGC) erbium-doped fiber amplifier (EDFA) for protection of surviving channels in a multiwavelength network in which several EDFA's are cascaded is studied. The effects of addition and/or dropping of wavelength channels in a network comprising six concatenated EDFA's have been analyzed by numerical simulation. Only the first EDFA in the cascade is gain clamped using a ring laser configuration. A large-signal numerical EDFA model which incorporates time variation effects and the downstream propagation of signal and pump and downstream and upstream propagation of amplified spontaneous emission (ASE) has been used. In particular, the effects of relaxation oscillations from the gain-controlled EDFA on the surviving channel protection are investigated. It is shown that power excursions caused in an eight-channel wavelength division multiplexed (WDM) network by the loss/addition of 6 channels will be lower than 1 dB and free of relaxation oscillations if the gain-controlled EDFA is strongly inverted and the average normalized population density of the metastable level does not drop below 0.74.
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