Multiple intermodal-vectorial four-wave mixing bands generated by selective excitation of orthogonally polarized LP and LP modes in a birefringent fiber.

This study investigates the nonlinear frequency conversions between the six polarization modes of a two-mode birefringent fiber. The aim is to demonstrate that the selective excitation of different combinations of linearly polarized spatial modes at the pump wavelength initiates distinct intermodal-vectorial four-wave mixing processes. In particular, this study shows that exciting two orthogonally polarized LP and LP modes can lead to the simultaneous generation of up to three pairs of different spatial modes of orthogonal polarizations at different wavelengths. The role of the phase birefringence of the spatial modes in the phase matching of such a four-wave mixing process is explained. Moreover, the theoretical predictions are verified through numerical simulations based on coupled nonlinear Schrödinger equations, and are also confirmed experimentally in a commercially available birefringent fiber.