Thermal Digital Imaging by Chirally Coded Metasurfaces

Chiral imaging, which utilizes chiral nanostructures to produce grayscale images, has attracted significant attention due to its potential for precise object and environmental perception. However, conventional chiral imaging techniques primarily rely on external light sources and other necessary optical components to create desired chiral patterns, which are compatible with device integration and miniaturization. In this study, a passive chiral imaging technique is presented by fully exploiting the spontaneous thermal emission of patterned metasurfaces to generate high-resolution chiral thermal images. It is shown that the circular dichroism of emitted thermal photons can be precisely engineered by controlling the degree of broken symmetries of resonant meta-atoms, achieving a wide range of tunability from 0 to 0.85 around 4 µm experimentally. Based on this approach, thermal metasurfaces encoded with distinct helicity states are fabricated to achieve passive high-resolution image encryption using thermal radiation. In addition, these findings demonstrate that chirality-based encryption is highly effective in reducing noise. The present study demonstrates the significant potential of integrating metasurface designs with thermal emission as a sophisticated framework for producing environmentally friendly, economically viable, and highly integrated optical devices and technologies.