Protection of surviving channels in all-optical gain-clamped lumped Raman fibre amplifier:: modelling and experimentation

In this article we investigate, both theoretically and experimentally, suppression of transient effects in all-optical gain-clamped (AOGC) lumped Raman fibre amplifiers (RFA) caused by channel addition/removal. Theoretical analysis of the AOGC lumped REA is based on numerical solution of coupled propagation equations for forward and backward propagating pumps, signals and spectral components of amplified spontaneous emission powers. In experimental verification, channel addition/removal was simulated by transmitting signals of two lasers through a counter-directionally pumped REA consisting of 16 km of dispersion compensating fibre (DCF). Light of one of the lasers was square-wave modulated at 500 Hz, power fluctuations of the other laser caused by cross-gain modulation of the REA were monitored at the output of the amplifier with a digital oscilloscope. All-optical feedback loop was implemented in the form of a ring laser. (C) 2003 Elsevier B.V. All rights reserved.