Ultra-broadband and high-efficiency planar chiral metamaterial.

To date, the helix-like assemblies are known for delivering the most broadband chiroptic response; however, as their dimensions shrink to the nanoscale, it becomes increasingly difficult to realize three-dimensional (3D) building blocks and accurate alignments. In addition, a continuous optical channel requirement hinders the downsizing for integrated photonics. Here, we introduce an alternative approach based on two assembled layers of dielectric-metal nanowires to demonstrate that chiroptic effects similar to helix-like metamaterials can be realized with an ultracompact planar structure by creating dissymmetry using orientation and making use of interference phenomena. We constructed two polarization filters for the near-(NIR) and the mid-infrared (MIR) spectrums that exhibit a broadband (0.835-2.11 µm and 3.84-10.64 µm) chiroptic response with maximum transmission and circular dichroism (CD) of approximately 0.965 and extinction ratio > 600. The structure is easy to fabricate, independent of alignments, and scalable from the visible to MIR range for applications including imaging, medical diagnostics, polarization conversion, and optical communication.