Generation of broadband terahertz focused vector beam using multifunctional metasurface

Focused vector beams are special beams with spatially inhomogeneous polarization distribution, which have broad application prospects in photonics applications such as high-resolution imaging, communications, and optical sensing. Recently, multifunctional metasurfaces for generating focused vector beams have attracted great interest due to their highly integratable, miniaturized, and compact properties. However, in terahertz (THz) range, related research remains largely unexplored. In this paper, a multifunctional broadband metasurface with an all-dielectric structure is proposed for generating focused vector beams in the terahertz region, enabling efficient linear polarization conversion and complete phase control of the transmitted field. Without the help of a polarization diversity scheme, this planar focused vector beam metasurface (FVBM) can simultaneously convert x- and y -polarized incident beams into focused radially polarized (RP) and azimuthally polarized (AP) beams, respectively. The simulation results show that the proposed metasurface exhibits excellent average conversion efficiencies (CEs) higher than 85.47% and 80.94% in the frequency range of 1.7 THz - 2.0 THz under linear x -polarized and y -polarized excitation, respectively. At 1.85 THz, the proposed metasurface can focus RP and AP beams with focusing efficiencies of 70.25% and 69.88%, respectively. The proposed metasurface has potential applications in integrating multiple functionalities into single, compact and ultrathin terahertz devices. • A multifunctional broadband terahertz metasurface is proposed by combining the low-symmetry design and mixed resonant modes. • The proposed metasurface can effectively control the polarization and phase simultaneously. • At 1.85 THz, the proposed metasurface can generate focused RP and AP beams with focusing efficiencies of ∼70.25% and ∼69.88%. • The focused RP and AP beams are generated with average CEs higher than 85.47% and 80.94% from 1.7 THz to 2.0 THz.