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

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 & DEG; & mu;m(-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.