Generation of terahertz vortex beams based on double-arrow-shaped metasurfaces

In this paper, a reflective double-arrow-shaped metasurface for generating vortex beams in the terahertz band is proposed. By applying Pancharatnam-Berry (PB) phase principle, a 2π phase gradient subarray consisted of four cycling units is designed at first, with reflection coefficient over 90%, and smooth phase shifts associated with axis rotation in 0.32-0.36 THz. Hereafter, a 21*21 array is formed with corresponding phase distribution and then effectively converts the circularly polarized waves into second-order vortex beams with a strong orbital angular momentum. This design exhibits the merits of simple structure, broadband bandwidth, and high efficiency.