Conversion of LP11 modes to vortex modes in an adiabatically twisted highly birefringent optical fiber

We experimentally demonstrate the possibility of adiabatic conversion of LP11 modes to vortex modes in a twisted highly birefringent fiber with a gradually increasing twist rate. Based on the values of effective indices, the LP11 modes are selectively converted to right-/left-handed circularly polarized vortex modes HE21 with a total angular momentum of ±2 and to quasi-TE01/TM01 modes with a total angular momentum of 0. The proposed conversion method has a purely topological origin, therefore, it is broadband in nature, in contrast to the methods based on resonant effects, and can be applied as an all-fiber broadband source of vortex beams. Funding: Narodowe Centrum Nauki (DEC-2016/22/A/ST7/00089, Maestro 8).