Cross modulation of pump-signals in distributed Raman amplifiers, theory and experiment

Cross modulation of the pump and signal in a backward pumped distributed Raman amplifier (DRA) is investigated theoretically and experimentally. An analytical theory describing the frequency response of cross modulation in a DRA with pump perturbation is developed for the first time. The corner frequency of this response is simply determined by the walkoff parameter of the two counterpropagation lights and the loss coefficient of the Raman fiber. This theory was confirmed by the agreement of theoretical results and experimental measurements.