Orbital‐Angular‐Momentum‐Encrypted Holography Based on Coding Information Metasurface

Metasurface holography has shown great potentials to reconstruct the full-wave information of electromagnetic (EM) waves, bringing benefits of high spatial resolution and good precision of reconstructed images. To obtain higher security of the metasurface holography, orbital-angular-momentum (OAM) of EM waves is taken into consideration as new freedom of the metasurface holography. The use two coding information metasurfaces is proposed to achieve the OAM-encrypted holography. One metasurface is used to generate different OAM beams with l = +/- 1 helical mode indices, which functions as the OAM feed; while the other is used to integrate different OAM helical-phase wavefronts into the holograms of the transmitted images, forming the OAM-encrypted holography. The predesigned images are accurately decoded only when the OAM-encrypted metasurface is illuminated by the incident OAM beams with the inverse helical mode indices (l = -/+ 1) under the incidence of defined polarization states. Experimental results agree well with the theoretical design and numerical simulations, verifying the feasibility and security of the OAM-encrypted holography. The proposed method will be a good candidate to enhance the secure communication systems and imaging systems.