3D metastructures enable time-programmable color encryption with built-in self-destruction

Mar 26, 2026

3D metastructures produce programmable structural colors for optical encryption, with a destruction mechanism that permanently erases data after readout.

(Nanowerk News) Researchers at City University of Hong Kong have developed three-dimensional metastructures, tiny engineered surface elements that manipulate light through their shape rather than through dyes or pigments, capable of producing programmable structural colors for optical encryption. The work, led by Professor Din Ping Tsai and co-author Zhi-Yong Hu of Jilin University, combines continuous color control, time-based encoding of multiple messages, and a physical destruction mechanism that erases information after readout. The study was published in Light: Science & Applications (“Time-programmable coloration via 3D metastructures for optical encryption”).

Key Findings

Conventional electronic encryption relies on mathematical algorithms that are increasingly threatened by advances in quantum computing. Loose key management practices can introduce further vulnerabilities. Optical encryption offers an alternative rooted in physical principles, encoding information across properties of light such as wavelength, polarization, and phase simultaneously. This multi-property encoding raises the difficulty of unauthorized decryption compared with single-channel electronic methods. Micro and nanostructures are especially attractive as encryption carriers because they control light purely through geometry, remain stable over time, and are environmentally safe. Yet most existing dynamic optical encryption approaches are limited to simple binary color switching triggered by a single parameter. That restriction caps both information capacity and resistance to brute force attacks that systematically test multiple parameters. A further weakness is that carriers typically survive intact after decryption, leaving the encoded information exposed to secondary leakage. Existing destruction methods often require chemical reactions or external energy and can introduce contamination or toxicity concerns. Professor Tsai’s team, based in the Department of Electrical Engineering and State Key Laboratory of Optical Quantum Materials at City University of Hong Kong, addressed these problems by designing metastructures whose color output is predictably controlled through precise geometric tuning. Under broadband white light, these structures shape the optical field to produce predefined colors and patterns visible at a distance. Under broadband white light illumination, the designed 3D metastructures precisely modulate the optical field to generate predefined colors and patterns in the far field. The enlarged inset illustrates the modulation mechanism of the structural colors produced by the 3D metastructures, where nenv1, nenv2 and nenv3 denote the environmental refractive indices corresponding to different device working environments. Morphological characterization of the chameleon-inspired patterned 3D metastructures is shown with scanning electron microscopy (SEM) images of the complete pattern and a magnified local region (bottom left). Time-programmable continuous color tuning achieved under varying environmental refractive indices is illustrated on the right, where T₁–T₇ represent the corresponding programmable time points. The bottom insets depict representative R/G/B output states under three distinct refractive index conditions. (Image: Reproduced from DOI:10.1038/s41377-026-02202-y, CC BY) (click on image to enlarge) Experiments confirmed that both single color and multicolor printing at high resolution could be achieved with strong color consistency and repeatability, establishing a reliable foundation for information encoding. To extend the technology toward anti-counterfeiting, the researchers built a recognition system based on deep learning. A convolutional neural network, a type of algorithm that automatically identifies visual features in images, extracts color distribution and spatial texture patterns from the structural color labels and classifies them into distinct categories. Unlike conventional methods that depend on manually set thresholds or isolated features, this approach maintained high recognition accuracy even under difficult conditions such as changing backgrounds, defocus, rotation, and localized contamination. The dynamic encryption behavior arises from changing the refractive index of the liquid surrounding the metastructures. Refractive index describes how much a material bends light. As the surrounding liquid changes, the structures respond by shifting their color output continuously along a predetermined path over time. Specific time windows labeled T1 through T7 in the experimental setup correspond to distinct decoded outputs, meaning a single physical carrier can deliver multiple messages in sequence. This substantially enlarges both the number of possible keys and the total information the system can carry. After the readout phase, evaporation of the surrounding liquid generates capillary forces, which are surface tension effects at tiny scales, that permanently collapse the nanostructures. This destroys the carrier without requiring added energy or chemical reagents, eliminating the risk of information leakage from a surviving carrier. The mechanism gives the system a physical burn after reading property. The surrounding environments in the experiments were characterized by three distinct refractive index conditions, denoted nenv1, nenv2, and nenv3, each producing different red, green, and blue output states. By uniting continuous color gamut control, programmable modulation over time, and irreversible erasure, the team demonstrated a multilayer encryption and stepwise decoding strategy. Different time windows yield different decoded content, while the destruction step renders the carrier permanently unreadable. This combination strengthens resistance to both brute force cracking and multi-parameter analytical attacks, presenting a proof of concept for erasable, high capacity optical encryption and anti-counterfeiting devices.