Impact of Brillouin Backscattering on Signal Distortions in Single-Fiber Diversity Loop Based Polarization-Insensitive FOPAs

We both experimentally and numerically investigate the impact of Brillouin backscattering in single-fiber-loop-based polarization-insensitive fiber-optical parametric amplifiers. We show that the loop configuration can cause distortions in the pump spectra due to Brillouin interactions of the counter-propagating pumps. This can result in significant distortions for amplified data signals at high gain when conventional highly nonlinear fibers are used. We thoroughly investigate the effect in experiments and derive a numerical model. This allows us to compare the results from system experiments with 28 GBd quadrature-phase shift keying signals to system simulations showing a good agreement on the system. Based on the model, we finally estimate that a large gain (~20 dB) with a low optical signal-to-noise ratio penalty (0.15 dB at bit error rate of 1 × 10
^-4
) for the amplified data signal should be possible in a single-fiber loop with Brillouin-suppressed highly nonlinear fibers.