Polarization-Insensitive Orbital Angular Momentum Converter Based on Helically Twisted Anti-Resonant Fiber

Based on the topological charge matching principle and mode coupling theory, the higher-order orbital angular momentum (OAM) generating mechanism in a helically-twisted anti-resonant fiber (HARF) is illustrated. We successfully fabricate a left-handed HARF by arc discharge method and excite the $\mathbf{OAM}_{-1}$ mode. The experimental result shows that the excitation of the $\mathbf{OAM}_{-1}$ mode is polarization-independent of input light and the polarization of the generated $\mathbf{OAM}_{-1}$ mode can be controlled by changing the polarization of the input light.