Vectorial Compound Metapixels for Arbitrary Nonorthogonal Polarization Steganography

Abstract

Malus’ law regulating the intensity of light when passed through a polarizer, forms the solid basis for image steganography based on orthogonal polarizations of light to convey hidden information without adverse perceptions, which underpins important practices in information encryptions, anti‐counterfeitings, and security labels. Unfortunately, the restriction to orthogonal states being taken for granted in the common perceptions fails to advance cryptoinformation to upgraded levels of security. By introducing a vectorial compound metapixel design, arbitrary nonorthogonal polarization multiplexing of independent grayscale images with high fidelity and strong concealment is demonstrated. The Jones matrix treatment of compound metapixels consisting of double atoms with tailored in‐plane orientation sum and difference allows point‐by‐point configuring of both the amplitude and polarization rotations of the output beam in an analytical and linear form. With this, both multiplexing two continuous grayscale images in arbitrary nonorthogonal polarization angles and concealing grayscale image on another in an arbitrary disclosure angle window are experimentally demonstrated in the visible TiO2 metasurface platform. The methods shed new light on multifarious metaoptics by harnessing the new degree of freedom and unlock the full potential of metasurface polarization optics.

Multifunctional Liquid Crystal Device for Grayscale Pattern Display and Holography with Tunable Spectral‐Response

“…Last but not least, the PCE and the holographic efficiency of the proposed multifunctional LC device are relatively high (100% and 81% in theory, 73.8% and 58.4% in experiment). We notice that there are some researches of polarization multiplexing and multifunctional image display in the field of metasurfaces [ 39 − 43 ] due to their ability of manipulating nanostructure's anisotropy arbitrarily. [ 44 ][ 45 ] However, the dual manipulations based on LCs are first proposed here and have the advantages of adjustable spectral response, large‐area manufacturing, high efficiency, and compatibility with existing commercial LCD devices.…”

Bilayer‐Metasurface Design, Fabrication, and Functionalization for Full‐Space Light Manipulation

“…Metasurfaces have been employed to precisely control the amplitude, [ 1–5 ] phase, [ 6–11 ] polarization, [ 12–17 ] and frequency [ 18–20 ] of incident light at the subwavelength resolution. Thanks to the powerful point‐to‐point manipulation capabilities at the subwavelength level of metasurfaces, lots of novel optical elements and devices including metalenses, [ 21–27 ] nanoprints, [ 28–34 ] meta‐gratings, [ 35–37 ] vortex‐beam generators, [ 38–41 ] meta‐holograms, [ 42–48 ] and encryption displays [ 49,50 ] have emerged over the past decade. However, due to the limited degrees of freedom of nanostructures, current light manipulation with metasurfaces is usually conducted in either transmission or reflection space while the other half of space is abandoned, which may hinder the improvement of information density and functionality of metasurfaces.…”

Manipulation of polarization conversion and multiplexing via all-silicon phase-modulated metasurfaces

“…Compared with conventional optical devices dependent on phase accumulation, metasurfaces can obtain abrupt phase change within subwavelength thickness by appropriately changing specific parameters, thereby generating various functions [4,5] . Specifically, metasurfaces can generate spatial phase discontinuities over the entire 2π range of a specific frequency, which have manifested that they can be utilized in a flat wave plate [6,7] , hologram imaging [8][9][10] , beam deflectors [11,12] , achromatic focusing lenses [13,14] , spin-orbital angular momentum manipulation [15][16][17][18] , and other fields.…”