Polarization control with dielectric helix metasurfaces and arrays

Using band structure analysis and reflectance spectrum simulations, we show that dielectric helices exhibit strong circular dichroism and have polarization stop gaps for light propagating perpendicular to the helices, despite the lack of helical symmetry along this direction. We apply perturbation theory to quantitatively explain these effects. We also demonstrate that even for a single layer of dielectric helices similar phenomena exist. As a result, the helix array can operate as a dielectric chiral mirror. This dielectric chiral mirror can completely reflect normally incident light with one circular polarization (right- or left-handed as determined by the handedness of the helices) without changing the polarization's handedness while allowing light with the opposite circular polarization to be entirely transmitted.