Time-domain characterization of transient effects and double Rayleigh backscattering noise in Raman amplifiers

Using a unified time-domain technique, we characterized and controlled Raman transient effects and double Rayleigh backscattering noise. Raman power transients and double Rayleigh backscattering noise were observed at the outputs of Raman amplifiers when square input pulses were applied to Raman amplifiers. A time-domain model was capable of describing the dynamics of the Raman amplifiers. Applying the model, we have constructed an effective transient control algorithm for distributed or lumped Raman amplifiers based only on output power monitoring. In an experiment, the control algorithm held gain fluctuations of surviving channels to less than =0.02 dB. The double Rayleigh backscattering noise was quantified by observing the pedestals at the Raman amplifiers outputs. We systematically showed the benefit of using a pump by-pass module, formed by an isolator and pump WDMs, in reducing the double Rayleigh backscattering noise.