Unraveling the Far-Field Coupling of Multilayered Chiral Metamaterials for CMOS-Enabled Midinfrared Imaging.

Three-dimensional (3D) chiral metamaterials are structures with broken out-of-plane symmetry. With intrinsic chirality, they present larger circular dichroism (CD) signals than the 2D chiral metamaterials. Among all types of 3D metamaterials, multilayer-stacked metamaterials stand out, as they have the potential for large-scale fabrication. To date, tremendous work has focused on improving the CD signal by trying different patterns and materials. However, they lack a general theoretical framework to bridge the in-plane pattern design and out-of-plane layer design. Besides, most attempts have been made on longer wavelengths, such as THz and GHz ranges, as resonator dimensions are challenging in shorter wavelengths. In this work, leveraging both in-plane rotation and out-of-plane twist designs, we explore the far-field coupling mechanism using temporal coupled-mode theory and discuss the mechanism behind the multilayered chiral metamaterials. Moreover, enabled by a standard CMOS fabrication process, we demonstrate multilayered chiral metamaterials in the mid-infrared regime. Furthermore, by arranging the achiral and chiral cells accordingly at different wavelengths, a 5 × 5 array is demonstrated for mid-infrared imaging. Our work has the potential to be used for free-space communication, optical encryption, and sensing applications.