Ultracompact metaimage display and encryption with a silver nanopolarizer based metasurface

Abstract

Governed by the Malus law, nanopolarizer-based metasurfaces can continuously modulate the intensity of incident linearly polarized (LP) light pixel-by-pixel, which has been applied to display metaimages with ultracompactness and high resolution. One unique characteristic of the Malus-assisted image display technique is that no matter the polarization direction of incident LP light, the image with different contrast always appears, which would affect the security of a metaimage. Here, inspired by the orientation degeneracy of the Malus law, we show that metaimage displays can be controlled in two fixed polarization directions, merely by reconfiguring the orientations of nanopolarizers. Specifically, for each metaimage pixel, there are two options for the orientation angle of the nanopolarizer corresponding to an equal grayscale value. By randomly selecting the orientation angle among two choices, the metaimage will be blurred or even hidden, except for the polarization direction of 0° for the original image and 90° for its contrast reversed partners. We experimentally demonstrate this concept by encoding a Lena image with pixels of 1000 × 1000 into a silver nanopolarizer-based metasurface and decoding/encrypting it in a polarization-controlled optical setup. The proposed metaimage display with the encryption functionality has advantages such as continuous grayscale modulation, ultrathinness, and high density, which can be applied in ultracompact image displays, high-end anti-counterfeiting, high-density optical information storage, information encryption, etc.