Optical Steganography Strategy Benefiting from Structural Color Cycling Based on Anodic Aluminum Oxide Membranes

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Optical steganography, as an important technology in information security, can be used in the field of image encryption. However, its cumbersome fabrication with high cost and an indistinguishable decryption effect severely hinder the scope of applications. In this study, structural color security engineering is proposed by employing multilayer stacks based on thin-film interference, which consist of an anodic aluminum oxide (AAO) membrane sandwiched between an ultrathin Ag layer and an Al substrate. Two hue cycles are defined by the gradient color rendering of samples. The multilayer stacks with various thicknesses of AAO membranes present visually equivalent colors from different hue cycles, which realize the ciphertext of “HEU” with a chromatic difference (Δ E ) of 3.25. It can be decrypted by the perturbation that is derived from the variation of the refractive index (RI) of such multilayer stacks and results in a maximum Δ E of 32.70 between the plaintext and the background. This convenient steganography technology based on the cyclical color rendering of high-purity colors realizes plaintext encryption and decryption effectively and benefits the clear identification of the information. This work paves the path to explore information security-related applications by structural color engineering.