Born–Kuhn‐Driven 2.5D Chiral Metamaterials

Abstract Chiral metamaterials (CMs) based on the Born–Kuhn (BK) model enable giant chiroptical responses but face fabrication complexity, structural limitations, and insufficient theoretical optimization. Here, ultrathin 2.5D BK‐based metamaterials is developed using shadow sphere lithography (SSL), overcoming traditional electron beam lithography constraints and costly alignment. The three‐layer rotated hole‐array (3RHA) structures, comprising rotated Ag/SiO ₂ /Au stacks (<100 nm thickness), achieve enhanced chiroptical performance ( g ‐factor = 0.6, CD/ t = 67°/µm) via optimized plasmon hybridization. Machine learning‐assisted parametric analyses identify optimal geometric parameters, validated experimentally. The 3RHAs showcase high sensitivity robustness in detecting chiral thalidomide enantiomers, facilitated by a second‐order norm ( L 2 norm) signal processing method. This scalable and precise approach significantly advances BK‐model CMs, providing a practical platform for ultrathin, high‐performance chiral photonic and sensing devices.