Modeling dynamic behavior of erbium-doped fiber amplifiers in all-optical ring networks

Erbium doped fiber amplifiers (EDFAs) are often used in multiwavelength networks. When these networks are reconfigured or when wavelength-channel failures occur, cross-gain modulation in the amplifiers causes power- fluctuations of the remaining channels. Up to now only result of dynamic models of a single EDFA and chains of EDFAs were presented in literature. We investigated the dynamic gain-behavior of EDFAs placed in a ring-network with respect to the effect of recirculating fluctuating crosstalk. For this purpose we implemented the electrical equivalent of an analytical dynamic EDFA-model into SPICE. Also optical add-drop multiplexer (OADM) functionality was transformed into an electrical equivalent. Rings and chains based on 1 to 9 OADMs, with an EDFA in each node were modelled. In the simulations two wavelength-channels were added and dropped, and the effect of a failure of one channel was investigated by monitoring the power of the remaining channel. We found that the rising-speed of the remaining channel power increases with the pass to drop power-ratio (which is actually the crosstalk to signal power-ratio, XSR). This means that a gain control to compensate for the power-fluctuations needs to be faster when EDFAs are configured in a ring-structure instead of a chain with the same number of EDFAs. The dynamic behavior of EDFAs in a ring-structure converges to that of EDFAs in a chain when the XSR reaches zero.