Large and tunable chiro-optical response with all dielectric helical nanomaterials

Controlling the state of optical polarization is a major focus of modern nanophotonics, which can be achieved quite effectively with plasmonic chiral nanomaterials, such as to obtain intense polarization sensitive optical response. Unfortunately, ohmic losses associated with light absorbed in metallic nanostructures can be a major limiting factor, which has triggered interest in alternate low-loss elements. Here, we describe an all dielectric chiral metamaterial comprising helical core–shell nanostructures, with large refractive index contrast between the core (SiO₂) and the shell (Si or Ge). The system exhibits very strong chiro-optical activity (differential transmittance ∼20%) whose spectral characteristics can be tuned by simply controlling the thickness of the shell, thereby covering the entire range from visible to near IR. The numerical calculations match well with the experimental results and suggest the chiro-optical response to originate in magnetic fields that were strongly confined within the nanostructures. Our fabrication method is wafer scale, and the material platform is CMOS-compatible, which together can allow a seamless integration of this novel material system to existing optoelectronic technologies.