Output Power and SNR Swings in Cascades of EDFA’s for Circuit- and Packet-Switched Optical Networks

A simple dynamic model of the erbium-doped fiber amplifier (EDFA) that includes self-saturation by amplified spontaneous emission (ASE) is used to analyze the power and signalto-noise ratio (SNR) transients in wavelength division multiplexed (WDM) optical networks in which signals cross chains of EDFA’s from source to destination. The model, which consists of solving sequentially one ordinary differential equation per amplifier, is used to 1) determine power and SNR excursions in the surviving channels along a chain of 35 EDFA’s during isolated add–drop events in a 16-channel WDM circuit switching scenario and 2) run Monte Carlo simulations of the first five EDFA’s of the same chain fed by burst-mode packet switching traffic on each of the 16 channels. Each packet source is modeled as an ON–OFF asynchronous transfer mode (ATM) source, with ON and OFF times having a heavy-tailed Pareto distribution. The aggregate source model is asymptotically self-similar, and well describes multimedia packet communications. The results are used to examine the influence of average network utilization and source ON–OFF time variance on the probability density function of signal power and SNR at each EDFA output. We demonstrate that selfsimilar traffic generates sizable power and SNR swings, especially at low network utilization. The simulations also indicate sizable broadening of the power and SNR density functions along the cascade of EDFA’s, reaching levels in excess of 9 dBm and 4 dB for the power and SNR swings, respectively, at the 5th EDFA. The effect becomes more pronounced for longer EDFA chains. Such a large broadening may imply serious system impairments in burst-mode WDM packet networks.