Reprogrammable meta-hologram for optical encryption

Abstract

Meta-holographic encryption is a potentially important technique for information security. Despite rapid progresses in multi-tasked meta-holograms, the number of information channels available in metasurfaces is limited, making meta-holographic encryption vulnerable to some attacking algorithms. Herein, we demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices. These two matrices are imposed to the incident light and the metasurface, respectively. While the all-dielectric metasurface is static, the phase matrix of incident light provides additional degrees of freedom to precisely control the eventual functions at will. With a single Si metasurface, arbitrary holographic images and videos have been transported and decrypted. We hope that this work paves a more promising way to optical information encryption and authentication.

Fig. 1. The working principle of reprogrammable meta-hologram.

a The schematic of the meta-holographic image with the modulated incident beam. b The holographic image of metasurface when it is illuminated with an incorrect uniform laser beam. The inset shows that the incident beam itself cannot provide correct information.

Fig. 2. The experimental demonstration of meta-hologram.

a The designed image, the simulated holographic image, and two separated phase profiles. b The top-view SEM of the Si metasurface. c Schematic for capturing the meta-hologram. d The recorded meta-holographic images with the designed incident beam (left), with a uniform laser beam (middle), and the image of incident laser itself (right). Here the lattice size is L = 240 nm.

Fig. 3. The vulnerable test of the meta-hologram.

From a–f, the mismatch ratio of the incident light increases from 0 to 50% with a step of 10%.

Fig. 4. The reprogrammable meta-hologram.

The holographic images of periodic element table. Each element in this table is one holographic image that is generated with the same metasurface in Fig. 2.