Removing the Directional Degeneracy of LP11Mode in a Fused-Type Mode Selective Coupler

Abstract

The removal of polarization and modal degeneracy in the excitation of higher order modes is realised in all-fiber mode-selective weakly-fused-couplers by controlling the coupler geometry. Experiments carried out with short couplers show strong polarization dependency, while long couplers with a slow varying cross-section have shown to remove polarization and spatial degeneracy in the first high order mode.