Vectorial Compound Metapixels for Arbitrary Nonorthogonal Polarization Steganography

• Published in: Advanced materials (Weinheim) 2021-10, Vol.33 (43), p.e2103472-n/a
• Main Authors: Deng, Zi‐Lan, Tu, Qing‐An, Wang, Yujie, Wang, Zhi‐Qiang, Shi, Tan, Feng, Ziwei, Qiao, Xiao‐Chen, Wang, Guo Ping, Xiao, Shumin, Li, Xiangping
• Format: Article
• Language: English
• Subjects: Gray scale; Luminous intensity; Materials science; metagratings; metasurfaces; multidimensional manipulation; Multiplexing; Optical polarization; Polarizers; Security; Steganography; Titanium dioxide; vectorial compound metapixels; vectorial holograms
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202103472

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. A vectorial compound metapixel design enables independent and linear modulations of the output beam in both amplitude and polarization rotations across the Malus metasurface. With this, arbitrary‐angle steganography is demonstrated by both multiplexing two continuous grayscale images in arbitrary nonorthogonal polarization angles and concealing one grayscale image on another in an arbitrary disclosure angle window.