Generalized Terahertz Perfect Vortices with Transmutable Intensity Profiles Based on Spin-Decoupled Geometric Metasurfaces

Perfect vortex beams (PVBs) possessing orbital angular momentum (OAM) and constant intensity profile enable practical applications in information encoding and transmission due to an unbounded number of orthogonal OAM channels and fixed annular intensity distributions. Geometric metasurfaces, which are 2D counterparts of metamaterials, have provided an ultra-compact platform to flexibly design perfect vortex beams in a single flat device. However, the previous reported PVBs based on geometric metasurfaces are limited to ring-shaped intensity profiles and intrinsic spin-coupling between two orthogonal spin-components. Here, spin-decoupled geometric metasurfaces encoding with two-step coordinate transformations are proposed to generate helicity-independent PVBs with transmutable intensity profiles. By tailoring local phase gradient along the azimuthal direction, spin-independent and polarization-rotated terahertz (THz) PVBs with C-N-fold rotationally symmetric intensity profiles have been theoretically designed and experimentally demonstrated. Furthermore, THz PVBs with arbitrary intensity profiles have also been realized. The unique approach for simultaneously manipulating the spiral phase, focusing phase, as well as intensity profiles will open a new avenue to develop multifunctional integrated devices and systems, which enables potential applications in information processing and optical communication.