Terahertz Encryption With a Polarization-Sensitive Metasurface.

The rapid advancement of information age has created an urgent need for integrated physical-layer security solutions. We propose a dual-functional terahertz (THz) encryption metasurface that enables independent information retrieval in both the near field and the far field within a single device. By precisely tailoring the complex amplitude of orthogonal linear polarization components, the metasurface forms two spatially separated far-field channels for left- and right-handed circular polarizations, which can be accessed simultaneously under linearly polarized illumination and are theoretically free from interchannel crosstalk. In the near field, polarization-selective amplitude modulation reveals textual patterns, whereas in the far field, phase engineering encodes multiple digital data in focal-spot arrays under linear, left-handed, and right-handed circular polarization states. This compact metasurface provides a scalable route toward THz security tags and robust physical-layer protection for identification, anticounterfeiting, and high-capacity wireless communications.