Enhanced visual cryptography utilizing spatial keys generated by optical metasurface

Owing to their inherent capability to manipulate multiple degrees of freedom of optical wavefronts, metasurfaces have emerged as a new-generation platform for information storage and transmission. Although multi-channel metasurfaces have been extensively explored for information multiplexing, plaintext data remain vulnerable to decryption once partial information leakage occurs. Visual secret sharing (VSS) encryption, recognized as a simple and efficient technique, can be further enhanced by integrating with multi-channel metasurface systems. In this work, a VSS encryption strategy based on an all-dielectric optical metasurface is proposed, featuring decoupled near-field and far-field responses. Two shared keys (SKs) are employed and separately assigned to the nanoprinting and holographic pathways. Retrieving the encrypted information requires independent decoding of the dual-channel signals, followed by an additional superposition operation. Both simulation and experimental results confirm the validity of the theoretical framework. The integration of VSS encryption with metasurface display technology significantly enhances encryption security, paving the way for further advancement of metasurface-based encryption techniques.