Non-reciprocal gain due to counter-propagating pumps in a polarization-independent FOPA with diversity loop

We investigate limitations set on single-pump polarization-independent fiber-optical parametric amplifier (FOPA) using polarization-maintaining highly nonlinear fiber in a diversity loop. We show that Brillouin scattering between the counter-propagating pumps yields polarization-dependent gain if an asymmetric local dispersion profile is present.