Rotatable Terahertz Vortex Field Based on Magneto-Optical Metasurface

Abstract

Terahertz vortex fields hold immense potential for wideband, high-capacity wireless communication. However, existing functional devices face challenges such as the lack of multi-channel multiplexing and active control capabilities. Here, a magneto-optical dielectric spiral metasurface that enables the generation and active rotation of vortex fields with different functionalities is proposed: within the frequency band of a completely orthogonal polarization conversion, the vortex beams excited by the two spin photonic states exhibit distinct topological charges with the mode purity of over 80% and focusing characteristics with spatial separation between them. In addition, within the frequency band of half orthogonal polarization conversion, a spiral field distribution can be obtained resulting from interference between the conversion and the direct-through components. By adjusting the magnetic field, the device allows dynamic, nonreciprocal rotation of both local polarization states and vortex fields. The rotation angle is determined by magnetization and topological charge with a maximum rotation of up to 180°. The magneto-optical light field manipulation mechanism offers promising applications in high-capacity communications, information encryption, and particle manipulation.