Abstract: The wavefront control of spin or orbital angular momentum (OAM) is widely applied in the optical and radio fields. However, most passive metasurfaces provide limited manipulations, such as the spin-locked wavefront, a static OAM combination, or an uncontrollable OAM energy distribution. We propose a reflection-type multi-feed metasurface to independently generate multi-mode OAM beams with dynamically switchable OAM combinations and spin states, while simultaneously, the energy distribution of carrying OAM modes is controllable. Specifically, four elements are proposed to overcome the spin-locked phase limitation by combining propagation and geometric phases. The robustness of these elements is analyzed. By involving the amplitude term and multi-feed technology in the design process, the proposed metasurface can generate OAM beams with a controllable energy distribution over modes and switchable mode combinations. OAM-based radio communication with four independent channels is experimentally demonstrated at 14 GHz by employing a pair of the proposed metasurfaces. The powers of different channels are adjustable by the provided amplitude term, and the maximum crosstalk is -9 dB, proving the effectiveness and practicability of the proposed method.

Key words: Orbital angular momentum (OAM); Geometric phase; Multi-feed metasurface; Spin-decoupled metasurface; Vortex beam communication

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