Vortex‐Vector Beam Conversion and Chiral Field Manipulation based on Terahertz Liquid Crystal Cascaded Metadevice

Abstract Vortex‐vector beam generators can effectively improve the channel capacity and communication accuracy, but they face the problems of narrow operating frequency band, low efficiency, and fixed function. Here, a terahertz liquid crystal cascaded metadevice is demonstrated, including a liquid crystal layer, an asymmetric metasurface layer, and a helical phase metasurface layer. The combination of liquid crystal's anisotropy and structural anisotropy from the asymmetric metasurface realizes the dynamic chirality construction. Then, the tunable chiral fields are effectively coupled with the helical geometric phase of the last metasurface layer to realize an active control between symmetric and asymmetric spin‐orbit angular momentum coupling, leading to the two types of beam generation and conversion: 1) spin‐dependent conversion and energy distribution between the vortex beams with ±2 topological charges; 2) the conversions between the 2‐order vortex beam and the cylindrical vector beam. The experimental results show that the excitation efficiency of vortex beams can reach over 92.1%, and the intensity modulation depth between different types of beams is more than 72.4%. This THz beam dynamic conversion mechanism and device scheme increase the degree of freedom of the device and have potential applications in terahertz multi‐channel wireless communication, polarization multiplexing imaging, and chiral spectrum detection.