Polarization-insensitive four-wave-mixing-based wavelength conversion in few-mode optical fibers

We report theoretical and experimental results on a wavelength converter based on inter-modal phase-matching in a graded index three-mode elliptical-core fiber. Here, two co-polarized pump waves propagate in one spatial mode whereas a signal and the corresponding generated idler propagate in another mode. We demonstrate that the idler power is independent of the signal polarization in both a 1 km and a 50 m long fiber. We attribute this polarization insensitivity to the fast random birefringence of the fiber under investigation in combination with the co-polarized pump configuration.