Cross-gain modulation effect on the behaviour of packetized cascaded EDFAs

Abstract

In this paper, we demonstrate the importance of the number of wavelength division multiplexing (WDM) channels and the network traffic variability on the dynamics of a cascade of erbium-doped fibre amplifiers (EDFAs) fed by packet traffic in burst mode. The dynamics are determined using a numerical model incorporating time variation effects in the EDFA. Calculations are based on the solution of a transcendental equation describing the time evolution of the reservoir, i.e. the total number of excited ions, for each EDFA. Traffic on WDM channels is modelled as statistically independent ON/OFF time-slotted sources. We find that the cross-gain modulation effect depends on the number of WDM channels and also on network traffic variability. As the number of WDM channels increases, and even though each one is highly variable in time, the dynamics of the total input power exhibits less fluctuation, allowing the reservoir to have a more suitable behaviour. In addition, the swings of the reservoir and the total output power decreases when we increase the network utilization factor. This positive effect is not felt on the output power excursion of an individual WDM channel. This is due to the fact that the cumulative effect of the reservoir fluctuations along a cascade will lead to further broadening of any individual channel power probability density function (PDF). Finally, we investigate the effect of gain clamping of the first amplifier in the cascade - by implementing a ring laser and propagating the lasing power through the cascade - on the statistics of several measurable entities.