Low index contrast all-dielectric helical structure for dual circular polarization manipulation

Abstract

All-dielectric photonic structures are normally constructed using materials of high refractive indices (n > 3) for enhanced properties at optical frequencies. In this study, we propose and numerically present the use of metasurface-like helices of lower index (n ∼ 1.5) for achieving enhanced chiral responses with low loss. The spatial organization of phase-shifted 3D helices gives rise to the emergence of effective structure with opposite handedness, where the unique symmetry further enables versatile dual circular polarization manipulation. With the elevated helices along with an elliptical cross-section, chiral properties can still be well-preserved in the presence of a similar low-index substrate. Our work has decent implications for 3D chiral device design as well as broadening the implementation horizon of low index dielectrics at optical frequencies.