High-Index Dielectric Metasurfaces: Unlocking Frontiers in Mid-Infrared Photonics

Metasurfaces, engineered planar structures manipulating light at subwavelength scales, have revolutionized nanophotonics across the visible to terahertz spectrum. All-dielectric material-based metasurfaces offer low optical losses, CMOS-compatible fabrication, and efficient light control via electric and magnetic resonances. The refractive index of such materials critically impacts the device performance, as traditional semiconductors like silicon and germanium provide moderate confinement, while emerging high-index materials such as WS2, PbTe, and GeSbTe enable stronger field localization and smaller device footprints. These high-index materials are vital for compact, reconfigurable metasurfaces operating in the mid- to far-infrared, essential for sensing, imaging, and thermal control. This article focuses on mid-IR photonics with dielectric metasurfaces, highlighting materials for high to ultrahigh refractive index with low losses, their advantages over plasmonics, and applications in wavefront control, nonlinear optics, and tunable devices. Future perspectives include scalable fabrication, AI-driven design, and broad industrial impact.