Abstract
We present an analytical study of multipath interference (MPI) in
pulse-pumped fiber Raman amplifiers (FRAs), caused by the internal
reflections from the fiber facets and the effect of Rayleigh backscattering.
For the first time, to the best of our knowledge, we derive a generalized
expression for the MPI-induced noise on signal in counter-pumped FRAs. The
obtained result takes into account four major sources of MPI, suggests their
physically transparent classification, and enables us to predict the FRA's
noise performance for an arbitrary modulated pump. Using the derived
expression, we characterize the MPI-induced noise in a typical 80-km span of
single-mode optical fiber.
Specifically, we examine the noise
enhancement in the pulse-pumped amplifier as compared to the amplifier
operating in the continuous-wave regime, and analyze its dependence on the
on-off gain and the pump-pulse duty cycle. We also estimate the impact of
the MPI-induced noise transfer on the amplifier's performance, and discuss
the optimal choice of pump modulation for different values of Q-penalty. The
results of our study are important for the design optimization of FRAs with
time-division-multiplexed pumping.
© 2010 IEEE
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