All-Fiber Fused Coupler for Stable Generation of Radially and Azimuthally Polarized Beams

The stable generation of TE01 and TM01 beams is demonstrated through a novel all-fiber fused coupler fabricated from a standard single mode fiber (SMF) and a custom air-core fiber. The fundamental mode in the SMF is directly coupled to the TM01 or TE01 mode by appropriately phase matching the modes in the fibers resulting in efficiency of similar to 67% and similar to 85%, and polarization purity of 70% and 82%, respectively. The phase matching is achieved through pre-tapering the SMF with precise control of the tapering ratio. The air-core fiber ensures selective excitation of the desired modes, thereby improving propagation stability and polarization quality of the TE01 and TM01 beams.