Acousto-optic generation of orbital angular momentum states of light in a tapered optical fiber

Abstract We demonstrate an acousto-optic mode converter based on a tapered optical fiber to efficiently generate orbital angular momentum states of light. In our scheme an acoustic wave is deployed to the waist of tapered optical fiber where two degenerate HE 21 modes leading to +1 and −1 orbital angular momentum eigen-modes are resonantly excited. The excitation of TM 01 and TE 01 modes is suppressed by enlarging the intermodal index difference between near-degenerate spatial modes. Numerical calculation for optimization of the taper diameter is provided. The experimental characterization of generated states is performed by analyzing the output far-field pattern and the spatial interference fringes with a uniform reference beam.