Surviving-channel-power transients in second-order pumped lumped Raman fiber amplifier:: Experimentation and modeling

In this paper, the effect of addition and/or dropping of wavelength-division-muitiplexed channels in an all-optical gain-clamped (AOGC) second-order (SO) pumped lumped Raman fiber amplifier (LRFA) has been investigated experimentally and analyzed by numerical simulation. Channel addition/removal was simulated by transmitting ten signals through a counter-directionally pumped LRFA consisting of a 16-km-long dispersion-compensating fiber. The light from eight lasers was square-wave modulated at 500 Hz; power transients of the surviving channels caused by cross-gain modulation of the LRFA were monitored at the output of the amplifier. All-optical feedback loop was implemented in the form of a ring laser. Gain-clamping properties of the SO-pumped LRFA are compared with those of the first-order pumped LRFA having the same ON/OFF Raman gain. Theoretical analysis of the AOGC LRFA was based on numerical 'solution of coupled propagation equations for the backward propagating pump, signals, and both forward and backward propagating spectral components of amplified spontaneous emission powers.