A research team led by Prof. Suseok Choi from the Department of Electrical Engineering at POSTECH has developed a programmable stretchable optical encryption technology based on stretchable multi-pixel and color-separation techniques. The research has been published online in March in Light: Science & Applications (LSA) (Impact Factor 20.6), a leading international journal in the field of optics published by Springer Nature.

The study was conducted by Seungmin Nam (first author; Ph.D. graduate of POSTECH and postdoctoral researcher, currently Assistant Professor in the Department of Electronic Engineering at Chosun University), Seohyun Woo (Integrated M.S.–Ph.D. student), and Jiyun Park (Ph.D. candidate) under the supervision of Prof. Choi.

With the rapid advancement of AI and digital technologies, the need for stronger and more sophisticated information security technologies has increased significantly. In particular, more complex and secure encryption methods are required to protect sensitive information. In this context, optical encryption technologies, which combine light and pattern information to reveal encrypted data only under specific conditions while keeping it hidden under other conditions, have recently attracted significant global attention.

Conventional digital encryption technologies rely on electrical semiconductor systems that process combinations of binary values (0 and 1). As computational capabilities—including those enabled by AI—continue to advance, such systems face increasing challenges in maintaining robust security. Therefore, encryption technologies with greater combinational complexity and more difficult decoding conditions are becoming increasingly important.

To address this need, the research team maximized encryption complexity by combining three controllable elements: stretchability, multi-pattern design, and multi-color responses. Unlike conventional stretchable systems that operate with simple on/off deformation, the proposed approach precisely controls specific strain levels during stretching. In addition, the pattern information consists of 4 × 4 pixel arrays (16 combinations), while the color response includes continuous wavelength variations across approximately 150 nm. By combining the number of stretching conditions, 16 pixel configurations, and wavelength variations within the 150 nm spectral range, the system achieves an extremely large number of possible encryption combinations. This enables encrypted information combined with Base64 codes to be revealed only under highly specific conditions.

Furthermore, the research team designed this complex programmable optical encryption system to be intuitively decoded through stretch-induced color changes, allowing the information to be retrieved visually when the correct encryption conditions are applied. The system also incorporates chiral liquid crystal elastomers (CLCEs)—materials capable of stretch-induced color changes—along with device-level design parameters such as material thickness. These material and structural combinations make the encryption scheme highly resistant to digital decryption or hacking attempts using conventional electronic, computational, or AI-based approaches.

This technology presents new possibilities for security encryption devices, optical computing, and analog computing, and is expected to be applicable to a wide range of future technologies.

This research was supported by the Samsung Science and Technology Foundation and by the Stretchable Technology Demonstration Program funded by the Korea Evaluation Institute of Industrial Technology (KEIT).