Broadband ContinuousInteger- and Fractional-OrderMultimode OAM Beam Generator via a Metasurface

Orbital angular momentum (OAM) waves have attracted significant attention for many applications, such as super-resolution imaging, image edge enhancement, and multiplexing communications, owing to their infinite orthogonal integer-order and nonorthogonal fractional-order modes. As a new degree of freedom for electromagnetic (EM) waves, multimode OAM beam generation is a precondition for their application. However, achieving multimode OAM beams simultaneously in free space is challenging. This study proposed a novel strategy for generating vortex beams with continuous OAM modes constructed from multiresonant metasurfaces of arbitrary shapes. The generator was capable of continuously generating an infinite number of OAM modes (α ∈ [1,3]) in the frequency range of 8 to 12 GHz. An experiment of broadband continuous integer- and fractional-order multimode OAM generators was successfully demonstrated to operate within the frequency range of 8 to 12 GHz. This study contributes to the reduction of the density and mass of generators and provides useful insights for radar detection systems and multiplexing communications.