Polarized Backward Raman Amplification in Unidirectionally Spun Fibers

The vector interaction of an intense, backwardpropagating, Raman pump and a weak, forward-propagating, Stokes signal in randomly birefringent, unidirectionally spun fibers is theoretically and numerically studied. The governing equations account for losses, Raman interaction, random linear birefringence, nonlinearity, and spinning. A model of birefringence, previously proposed for determining the polarization properties of unidirectionally spun fibers, is applied to the Raman amplifier confirming that this particular spin generates an equivalent circular birefringence. Numerical solutions show that, for rapid spinning, random birefringence effects are greatly reduced, Raman gain can be enhanced, and its fluctuations are minimized.