A framework based on metasurfaces for dynamic angular momentum holographic encryption

Abstract

Angular momentum (AM) holography encodes information onto a single metasurface, encompassing both the spin and orbital AM dimensions of light, providing a high-dimensional space for optical encryption. However, the trade-off between the ever-increasing channel multiplexing capacity and the computational cost of generating the required phase distribution in real time limits existing AM encryption schemes to static, offline-designed architectures with fixed key mappings. This paper proposes a Dynamic AM Holographic Encryption (DAHE) framework that co-designs fast phase synthesis and time-varying key derivation on a non-interlaced metasurface platform. The dual-domain wavelet attention network generates the basic phase hologram in approximately 221 ms per channel on a single Graphics Processing Unit, while the Transformer-based module derives a non-repeating optical key set from a timestamped user identifier within 5 ms. Both outputs are fed into a deterministic overlay layer where we propose a comb-convolutional spiral phase encoding strategy. By convolving the spiral phase with a two-dimensional Dirac comb function, the orbital AM singularity is replicated on a periodic local central lattice, thereby achieving efficient multi-channel AM multiplexing across the entire monolithic metasurface and producing the final multiplexed metasurface phase. Multi-user time-varying access experiments confirm that correct image reconstruction requires valid user identity, timestamps, and matching AM optical states simultaneously; unauthorized or time-mismatched queries only return noise. The DAHE framework combines real-time holographic phase engineering with updatable cryptographic key management, opening a practical pathway for dynamic secure displays and optical authentication.