Manipulation of Orbital Angular Momentum Spectrum Using Shape‐Tailored Metasurfaces

Abstract Vortex beams carrying orbital angular momentum (OAM) are widely applied in various electromagnetic, optical, and quantum systems. A tailored OAM spectrum composed of several specific modes as expected holds a promise for expanding the degrees of freedom of the systems. However, such a broadband high‐purity tailored spectrum is difficult to be achieved by the present devices, where the broadband amplitude manipulation is not explored yet. In this work, inspired by the envelope‐modulation theory, an elegant and universal way to manipulate the OAM spectrum in wide bandwidth is proposed by using a shape‐tailored metasurface. First, the rotating meta‐atoms on a triangular lattice are proved to have smaller coupling distortion than that on a square lattice, and this behavior is critical for high‐purity vortex spectrum generation by the Pancharatnam–Berry‐based metasurfaces. Second, a universal modulation relation is established between the spatial arrangement of metasurfaces and the generated vortex beams. Finally, the broadband‐modulated OAM spectra and the comb‐like OAM spectra are theoretically and experimentally demonstrated by the shape‐tailored metasurfaces. The proposed amplitude‐modulation scheme offers a novel concept and engineering route to manipulate the OAM spectrum in wide bandwidth, which can promote the development of OAM‐based applications.