Four-channel Imaging Based on Reconfigurable Metasurfaces: Hyperchaotic Encryption under Physical Protection

Metasurfaces facilitate high-capacity optical information integration by simultaneously supporting near-field nanoprinting and far-field holography on a single platform. However, conventional multi-channel designs face critical security vulnerabilities for sensitive information due to insufficient encryption mechanisms. In this work, we propose a four-channel phase-change metasurface featuring algorithm-physical co-security-a dual-protection framework combining intrinsic metasurface physical security with chaotic encryption. Our polarization-multiplexed metasurface generates four optical imaging channels through meta-atom design, including two far-field holograms and two near-field patterns. To enhance system security, we apply Chen hyperchaotic encryption combined with the Logistic map and DNA encoding to convert near-field information into secure QR codes; far-field holograms are retained to demonstrate the metasurface’s information capacity and for attack detection. Phase-change metasurface further provides physical-layer security by dynamically switching imaging channels via crystalline-to-amorphous state transitions, enhancing anti-counterfeiting and reliability. The proposed metasurface achieves high-fidelity imaging, robust anti-attack performance, and independent channel control. This integrated approach pioneers a secure paradigm for high-density optical information processing.

💡 Research Summary

The paper presents a novel four‑channel optical information platform that merges metasurface engineering, hyperchaotic encryption, and phase‑change material–based physical security. A polarization‑multiplexed metasurface is designed using a double‑cell nano‑pillar architecture made of Sb₂S₃ on SiO₂. By independently controlling the Jones‑matrix elements tₓₓ and tₓᵧ through the orientation angles (θ₁, θ₂) and phase responses (ϕₓ, ϕ_y) of the two pillars, the device simultaneously generates two far‑field holograms (a “boat” image under x‑polarization and an “NCU” logo under y‑polarization) and two near‑field QR‑code patterns (one for each polarization). The metasurface achieves near‑unity transmission and a full 0–2π phase coverage at 633 nm, ensuring high‑fidelity imaging; the far‑field holograms also serve as visual tamper‑indicators.

Security is provided on two layers. The near‑field QR codes are encrypted with a hybrid algorithm that combines a classic Logistic map (μ = 3.99), the four‑dimensional Chen hyperchaotic system (a = 35, b = 3, c = 28, d = 5), and DNA encoding. A 32 × 32 grayscale plaintext image is first transformed into a binary stream; the Logistic map yields a sequence L, while the Chen system generates sequences X, Y, Z, and M. Sequence X selects one of eight DNA encoding rules, converting bits into nucleotides (A, T, C, G). Sequence Y governs DNA operations (complement, reverse, etc.), Z determines arithmetic/logic operators (ADD, SUB, XOR), and M controls the final decoding back to grayscale. The result is a continuous‑tone ciphertext that is subsequently reshaped into a binary QR pattern, embedding the chaotic keys within the QR code itself. This approach relaxes the metasurface’s requirement for precise grayscale reproduction because the QR code is inherently binary and tolerant to optical noise.

Physical protection is achieved by exploiting the reversible amorphous‑to‑crystalline phase transition of Sb₂S₃. In the amorphous state the metasurface exhibits high transmission and the designed phase profiles, enabling all four channels. Switching to the crystalline state dramatically reduces transmission, effectively disabling both holographic and QR‑code outputs and rendering the stored information inaccessible. The transition can be induced electrically or thermally, providing an on‑demand “lock” mechanism that is unclonable and resistant to counterfeiting.

Experimental results show that the near‑field QR channels reach a structural similarity index (SSIM) of 0.99, while the far‑field holograms achieve SSIM values of 0.8543 and 0.7204 respectively. Key‑sensitivity analysis demonstrates that minute variations (≈10⁻⁶) in the chaotic parameters produce completely different ciphertexts, confirming a large key space. Statistical tests (NIST randomness, histogram uniformity, pixel‑correlation) verify the randomness of the encrypted images, and the system resists common attacks such as brute‑force, statistical analysis, and cropping. Moreover, any tampering with the metasurface is instantly visible in the far‑field holograms, offering a rapid visual alarm.

In summary, the work integrates (1) a polarization‑multiplexed, double‑cell metasurface capable of four independent high‑resolution imaging channels, (2) a hyperchaotic‑DNA hybrid encryption scheme that secures near‑field QR data while easing fabrication tolerances, and (3) a reversible phase‑change material that provides a physical “on/off” security layer. This dual‑layer co‑security paradigm advances high‑density, tamper‑evident optical information processing and opens pathways for secure displays, data storage, and communication systems where both algorithmic and physical protections are required.