Spin-enabled terahertz quasicrystal metasurface for orbital angular momentum engineering

Quasicrystal lattice characterizes long-range order configuration, but lacks translational symmetry, exhibiting in particular a high-order rotational symmetry, which is distinct from conventional crystals. Multi-dimensional-designable quasicrystal metasurface provides a powerful platform for the orbital angular momentum (OAM) spatial manipulation of terahertz (THz) beams. This work numerically demonstrates a vortex beam emitter in the THz regime based on silicon quasicrystal metasurfaces. By implementing the Penrose tiling arrangement with fivefold rotational symmetry, the proposed OAM meta-device breaks the design constraints of traditional periodic metasurfaces, enabling selective excitation and flexible control of orbital angular momentum modes. Theoretical and numerical analyses demonstrate that these quasicrystal metasurfaces not only realize both first- and higher-order vortex beams efficiently, but also exhibit favorable broadband response and structural robustness. Furthermore, their non-periodic nature provides new degrees of freedom for wavefront manipulation, which reduce the arrangement density of micro-atoms significantly. This work provides enhanced design freedom for highly integrated, multifunctional optical devices, with promising applications in optical communications, quantum information processing, and micro-nano optics.