Novel approach for polarization-sensitive measurements of transverse modes in few-mode optical fibers

We report for the first time on the polarization analysis of higher-order modes in a few-mode optical fiber using a three-mirror ring resonator. Higher-order fiber modes were generated by carefully squeezing the fiber. The power fraction of the dominating modes was measured, and we determined the polarization state which is different for each mode due to transverse variations of birefringence in the fiber.