A highly tunable sub-wavelength chiral structure for circular polarizer

Chiral structures are composed of periodically arranged asymmetric particles. The asymmetry of chiral particles results in extraordinary properties like negative refraction index, giant optical activity and circular dichroism. Consequently, they have applications in super lens and various polarization controllers. There are two types of chiral structures, namely planar and 3D structures. The planar ones usually have three- or fourfold rotational symmetry, which limits the polarization tuning capability. On the other hand, the 3D prototypes are difficult to fabricate and measure. Here, we propose a highly tunable sub-wavelength 3D chiral structure. It can be conveniently manufactured on the single-layer double-side printed circuit board. Based on the proposed idea, a sample converting a linearly polarized wave to a circularly polarized one is demonstrated both theoretically and experimentally. The conversion efficiency is measured to be 60%.