Metamaterials: Giving light another new twist, chirality
After years of doubt, the scientific community now embraces the almost paradoxical properties of metamaterials, also known as negative index materials (NIMs). The unusual properties of fabricated NIMs include perfect lensing (beating the diffraction limit for electromagnetic waves), zero reflectance, and negative Snell’s law angles. Acceptance of these phenomena has come with recent design, fabrication, demonstration, and detailed first principles simulations for operation at microwave and THz frequencies from the Ames Laboratory group. More recently, a negative index of refraction due to chirality is first demonstrated for a bi-layered metamaterial based on pairs of mutually twisted planar metal patterns in parallel planes, which also shows strong optical activity and circular dichroism. If these chiral structures could be further engineered to work in optical and visible frequency ranges, strong optical activity might enable novel optical devices, such as ultra-thin circular polarizers and polarization rotators.
In this figure, we present the designs and the fabricated samples for GHz and THz frequencies. Notice the rotation angle per wavelength is around 800o for GHz frequencies, around 400o for 3 microns and around 60o for 1.5 microns. The rotation angle is given with zero ellipticity, i.e., it means the linear polarized wave rotates and remains linear polarized. These new designs, which have been fabricated and measured experimentally, can be used as thin-film optical isolators.
Relevant Publication(s): M. Decker, R. Zhao, C.M. Soukoulis, S. Linden and M. Wegener, Opt. Lett. 35, 1593 (2010); Z. Li, R. Zhao, Th. Koschny, M. Kafesaki, E. Colak, H. Caglayan, E. Ozbay, C.M. Soukoulis, Appl. Phys. Lett., 97, 081901 (2010).