Multichannel Linear and Nonlinear Information Encryptions with Malus Metasurfaces

Abstract The superior capability of wavefront manipulation makes metasurfaces a promising platform for implementing high‐density information storage and multifold optical encryption. Although some metasurfaces have realized information encryption, it is still challenging to implement polarization‐encrypted grayscale images in both linear and nonlinear channels. Here, a novel approach to realize multichannel linear and nonlinear information encryptions is proposed based on nonlinear Malus metasurfaces composed of single‐sized meta‐atoms, in which the polarization states of the linear and nonlinear signals can be decoupled. As a proof of concept, two distinct grayscale images with different polarizations have been encrypted in the fundamental and second harmonic wave channels simultaneously. Besides, by further introducing the nonlinear Pancharatnam‐Berry phase, a tri‐channel polarization encrypted metasurface with a multi‐level grayscale image in the near field and two holographic images in the far field has been experimentally demonstrated at the second harmonic frequency. This work provides more degrees of freedom for multichannel information storage and opens an avenue for optical information encryption in both linear and nonlinear regimes.