Fast power transients in Raman fibre amplifiers

We have investigated, both experimentally and theoretically, the effect of channel removal/addition on surviving channel power transients in distributed Raman fibre amplifier (RFA). Signals from two laser diodes were transmitted through counter-directionally pumped RFA consisting of 15.6 km of dispersion compensating fibre (DCF). Light of on of the laser diodes was square wave modulated at 500 Hz to simulate channel addition/removal. At the output of the RFA, the modulated channel was eliminated with an optical band-pass filter and power fluctuations of the c.w. channel were recorded with a high speed digital oscilloscope. Output power transients in RFA were studied theoretically using a large-signal numerical model that includes time variation effects and takes into account pump-to-pump and signal-to-signal interactions and generation of amplified spontaneous emission.