Gallium arsenide-enabled spatial-polarization-frequency multiplexing metasurface for terahertz encrypted communication

Abstract

Robust information security is a fundamental imperative for all facets of the modern digital society. To address this critical need, we introduce a spatial-polarization-frequency multiplexing metasurface enabled by gallium arsenide (GaAs) for terahertz encrypted communication in this paper. The incorporation of GaAs and vanadium dioxide (VO₂) as active materials enables independent control for 16 channels. In detail, GaAs transitions to a low-resistivity state under optical pumping. The metasurface independently manipulates incident waves at 0.76 THz and 1.32 THz, each with selectable x-LP or y-LP, propagating along ± z directions to generate 8 channels. Without optical pumping, GaAs transitions to a high-resistivity state. While VO₂ is in the insulating state, the metasurface independently manipulates incident 0.9 THz waves with x-LP and y-LP polarization propagating along ± z directions, yielding 4 channels. While VO₂ is in the metallic state, the metasurface reconfigures its phase distribution along ± z directions respectively, generating an additional 4 channels. Thus, these 16 channels can generate distinct holographic images representing alphanumeric characters (A-F, 0–9), each corresponding to a unique Base-16 encoding symbol. During communication, the receiver must utilize the unique metasurface as a physical key for successful decryption. In addition, decryption strictly requires predetermined conditions including specific incident direction, operating frequency, polarization signature, and phase transition state of the active materials. These combined requirements act as multiple locks, significantly boosting the security of the optical communication approach.