Low-Profile Two-Dimensional THz Airy Beam Generator Using the Phase-Only Reflective Metasurface

This paper presents a low-profile 400 GHz Airy beam generator using a reflective anisotropic metasurface based on a phase-only modified Fourier-transform-type method. To efficiently launch 2-D terahertz (THz) Airy waves of compact size, the proposed Airy-beam system adopts a folded topology consisting of a single-layered reflective metasurface and a polarizing grid. Different from the conventional dielectric lens or single-layered transmitting metasurface, the proposed folded reflective structure achieves the required cubic phase using a quartz-based reflective metasurface with reduced volume and increased efficiency. A quasi-I-shaped unit cell is proposed for the metasurface to manipulate the incident THz wave by efficiently converting the initial illumination to its cross polarization and simultaneously adjusting its phase with a range of $2\pi $ . A reflective metasurface and a THz polarizing grid are designed and integrated to show both the unique transverse acceleration behavior and the self-reconstruction property at the 400 GHz band. The simulated and measured results demonstrate that the proposed folded topology can produce the expected THz Airy beam with compact size and polarization conversion efficiency over 90%.