A Reflective Metasurface for Flexible Control of Divergence Angles in Orbital Angular Momentum Beams

To address the challenge of multi-mode OAM wave reception caused by varying divergence angles in orbital angular momentum (OAM) beams with different topological charges, this paper proposes a novel method to control the divergence angles of OAM beams. A geometric framework enabling identical divergence angles for different OAM modes is established, resolving a critical issue in multi-mode systems. This approach integrates one-dimensional linear array theory with the design of equal-divergence-angle OAM beams. Precise divergence angle control is achieved by adjusting element phases without altering the metasurface structure. Following this approach, a metasurface reflector is engineered to produce orbital angular momentum beams with uniform divergence angles. Comprising a 30×30 metal-insulator-metal array, the metasurface independently manipulates electromagnetic waves (EMWs) of dual polarizations. By incorporating divergence angle regulation factors into phase design, the proposed reflective metasurface produces dual-polarization, dual-mode OAM waves with tunable equal divergence angles. This design offers an effective technique for flexible control of multi-mode OAM beam divergence angles, facilitating simplification of receiver devices in OAM-based communication systems.