Ultrathin Twisted Stacked Gap‐Plasmon Metasurface with Giant and Tunable Shortwave Infrared Chirality

Abstract Ultrathin optical components with giant circular dichroism hold great promise for polarization‐sensitive nanophotonics. However, existing chiral metamaterials often rely on complex‐shaped nanoinclusions, and there remains a paucity of designs active in the shortwave infrared (SWIR) useful for telecommunication and night vision. Here a detailed numerical analysis of the chiroptical response of a simple twisted stacked variant of gap‐plasmon metasurface is presented based on periodic nanohole arrays. Impressively, the 100‐nm free‐standing plasmonic metasurface can attain a thickness‐normalized ellipticity of up to 74.2° µm⁻¹ with tunable bands in the SWIR. Strong and robust optical activity is achieved through energy confinement by gap surface plasmons and effective inter‐nanohole coupling, resulting in an intense superchiral near field. The ultrathin plasmonic metasurface serves as an excellent platform for refractive index sensing with a sensitivity S_n of up to 648.1 nm RIU⁻¹ and field‐enhanced enantiodiscrimination. The simple metasurface with strong SWIR chirality can enjoy a multitude of potential applications including polarization‐sensitive photodetection, optical telecommunication, machine vision, medical imaging, and spectroscopy. These findings also offer insights into some fundamental design principles for twisted stacked aperture‐based metasurfaces and should facilitate the development of new chiral metamaterials with exceptional performance.