Phase-Change Metasurfaces for Dynamic Image Display and Information Encryption

Optical metasurfaces enable us to engineer the electromagnetic space and control light propagation at an unprecedented level, offering a powerful tool to achieve modulation of light over multiple physical dimensions. Here, we demonstrate a $\mathrm{Sb}$${}_{2}$$\mathrm{S}$${}_{3}$ phase-change metasurface platform that allows active manipulation of both the amplitude and the phase. In particular, we implement dynamic nanoprinting and holographic image display through the tuning of the crystallization levels of this phase-change material. The $\mathrm{Sb}$${}_{2}$$\mathrm{S}$${}_{3}$ nanobricks tailored to perform the amplitude, geometric, and propagation-phase modulation constitute the dynamic meta-atoms in the multiplexed metasurfaces. Using the incident polarizations as decoding keys, the encoded information can be reproduced in the form of a nanoprinted grayscale image in the near field and two holographic images in the far field. These images can be switched on and off by taking advantage of the reversible tunability of the $\mathrm{Sb}$${}_{2}$$\mathrm{S}$${}_{3}$ nanostructure between the amorphous and crystalline states. The proposed phase-change metasurfaces featuring manifold information and multifold encryption promise ultracompact data storage with high capacity and high security, which suggests an exciting direction for modern cryptography and security applications.