Analysis of channel addition/removal response in all-optical gain-clamped cascade of lumped Raman fiber amplifiers

The effect of addition and/or dropping of wavelength-multiplexed channels in a network comprising three concatenated lumped Raman fiber amplifiers (LRFAs) have been analyzed by numerical simulation and verified experimentally. The first LRFA in the cascade is gain clamped using a ring-laser configuration, and the lasing power propagates through the cascade. A large-signal numerical model that incorporates time variation effects and the downstream propagation of signal, upstream propagation of pumps, and downstream and upstream propagation of amplified spontaneous emission spectral components has been used for the theoretical analysis. The LRFAs consist of 16 km of dispersion-compensating fiber counterdirectionally pumped at 1455 nm by a Raman fiber laser. Channel addition/removal is simulated by propagating through the cascade of LRFAs optical power from two laser diodes. One of them is square-wave modulated at 500 Hz, and power fluctuations of the second continuous-wave signal caused by the cross-gain saturation effect in LRFAs are monitored.