Multi‐Dimensional Near‐/Far‐Field Holography Enabled by On‐Chip Metasurface for Information Encryption

On‐chip metasurfaces, as miniaturized optical devices, show great potential in information security due to their compact structure and excellent multiplexing capabilities. Achieving holographic multiplexing across different operational spaces with a single metasurface can significantly enhance multiplexing dimensionality and channel capacity. However, limited by guided‐wave excitation modes, this approach remains underexplored. This paper proposes a scheme integrating Fresnel (near‐field) and far‐field holography on a single on‐chip metasurface, distributing four multiplexing dimensions across two operational spaces. Using orthogonal detour phases and wavelength‐dependent accumulation phases in meta‐atom design, we achieve wavelength, direction, and distance multiplexing in the Fresnel region. Furthermore, by linking meta‐atom displacement to the incident azimuth of guided waves, far‐field multiplexing is extended to wavelength, direction, and azimuth dimensions. As proof of concept, we demonstrate an encryption strategy via simulations of 10‐channel Fresnel holography and 2‐channel far‐field holography. Decryption mandates collaboration of two authorized parties to reconstruct the plaintext in the Fresnel region following the far‐field pattern sequence, ensuring high physical security. Since multiplexing dimensions in the two operational spaces differ, the risk of information cross‐leakage is effectively mitigated. This hybrid scheme enhances both information capacity and encryption security, offering a viable pathway toward high‐security optical information systems.