A Novel Method for Controlling the Divergence Angle of Multimode Vortex Beams

This letter proposes a new method for controlling the divergence angles of multimode orbital angular momentum (OAM) vortex beams. A geometric framework is established that allows for the same divergence angle across different OAM modes, which addresses a significant challenge in multimode systems. Proposed method combines 1-D linear array theory and the design of OAM beams with an equal divergence angle. By adjusting element phases, precise divergence control is achieved without altering the metasurface structure. The method's effectiveness is verified through theoretical synthesis, full-wave simulations, and experimental validation. This approach offers accurate control over a wide range of angles, demonstrating potential applications in communication systems.