Active Broadband Terahertz OAM-Based Metalens Based on Multi-Channel Multiplexing

Abstract

Vortex beams with orbital angular momentum (OAM) exhibit immense potential in various fields such as communications, information processing, and optical tweezers. Nevertheless, current terahertz vortex beam generators still face challenges including narrow frequency bands, low efficiency, limited multiplexing capabilities, and difficulties in dynamic tuning. Here, the study introduces a new electrically controlled multi-channel multiplexing strategy that harnesses cascaded helical geometric metasurface, liquid crystal (LC) layer, and OAM-based metalens to achieve comprehensive and independent phase manipulation across all four spin channels. Moreover, by employing spin, spatial, OAM multiplexing, and the LC active control technology, eight distinguishable spin angular momentum (SAM)-OAM coupling states are decoded, enabling dynamic control of vortex beams with 6 different topological charges. Experimental validation reveals remarkable performance: within the broadband range of 0.4–0.6 THz, the vortex beams exhibit a peak excitation efficiency of up to 94%, with each mode purity reaching its highest level of >80%, and the minimum value of inter-mode coupling crosstalk is <–11 dB. This terahertz vortex beam generation and conversion mechanism enhances the operational flexibility in light field manipulation, breaking through the limitations of channel multiplexing and dynamic manipulation in the terahertz band, pioneering a novel avenue for bolstering parallel processing, mitigating inter-channel crosstalk.