Generation of terahertz vector beams using dielectric metasurfaces via spin-decoupled phase control

TLDR

Cylindrical vector beams, with spatially varying polarization, are promising for photonics applications such as imaging, plasmon excitation, optical trapping, and laser machining, and while metasurface generation of CVBs has attracted interest for its design flexibility, it has yet to be explored in the terahertz regime. The study proposes and experimentally demonstrates a generic method to efficiently generate terahertz cylindrical vector beams carrying orbital angular momentum using transmission-type spatial‑variant dielectric metasurfaces that manipulate interference between two circularly polarized transmission components. The method employs spin‑decoupled phase control by simultaneously manipulating dynamic and geometric phases of each structure, enabling the design of polarization‑dependent terahertz vector vortex and Bessel beams, which are experimentally characterized. The method enables versatile generation of terahertz vector beams, opening avenues for compact, high‑performance devices across broad electromagnetic spectra.

Abstract

Abstract Cylindrical vector beams (CVBs), being a special kind of beams with spatially variant states of polarizations, are promising in photonics applications, including high-resolution imaging, plasmon excitation, optical trapping, and laser machining. Recently, generating CVBs using metasurfaces has drawn enormous interest owing to their highly designable, multifunctional, and integratable features. However, related studies remain unexplored in the terahertz regime. Here, a generic method for efficiently generating terahertz CVBs carrying orbital angular momentums (OAMs) is proposed and experimentally demonstrated using transmission-type spatial-variant dielectric metasurfaces, which is realized by designing the interference between the two circularly polarized transmission components. This method is based on spin-decoupled phase control allowed by simultaneously manipulating the dynamic phase and geometric phase of each structure, endowing more degree of freedom in designing the vector beams. Two types of metasurfaces which respectively generate polarization-dependent terahertz vector vortex beams (VVBs) and vector Bessel beams (VBBs) are experimentally characterized. The proposed method opens a new window to generate versatile vector beams, providing new capabilities in developing novel, compact, and high-performance devices applicable to broad electromagnetic spectral regimes.