Generating a multi-mode vortex beam based on spoof surface plasmon polaritons.

The vortex beam provides a promising alternative for next-generation wireless communication, but it is a long-standing challenge to generate a multi-mode and robust vortex beam. In this Letter, a multi-mode vortex beam emitter is introduced and experimentally verified based on spoof surface plasmon polaritons (SSPP). The SSPP on a helical grating carries multi-mode orbital angular momentum and can be converted into a high-purity vortex beam via the diffraction of a ring array. The operation frequency and topological charge are determined by that of the SSPP. This emitter can achieve the function of beam-scanning in each radiation band. The beam-scanning and vortex characteristics are experimentally verified. The designed emitter is compact and robust, and we are confident that this work will have great application prospects in communication systems.