The impact of signal double Rayleigh scattering
(DRS) noise in time-division multiplexed counterpropagating
Raman pumping schemes is theoretically and experimentally
investigated. We show that, for small pump modulation duty
cycles, DRS noise can be greatly enhanced with respect to
continuous-wave pumping. By increasing the pump modulation
frequency, however, this detrimental effect is effectively reduced,
providing a powerful technique for noise figure equalization and
pump four-wave mixing suppression in large bandwidth discrete
and distributed amplifier
