title: On metamaterial circular polarizers based on metal N-helices.
abstract: Metal-helix based metamaterials have been introduced as compact and broadband circular polarizers. However, the end of the metal wire together with the helix center defines an axis in space, which unavoidably breaks the rotational symmetry at the metamaterial surface. This introduces linear birefringence. Symmetry can be recovered by considering an integer number, e.g. N = 4, of intertwined helices arranged to a square array. We show that the operation principles are fundamentally different though. Metamaterial circular polarizers based on N = 4 helices, unlike single helices, inherently require absorption of the constituent metal. Otherwise, the combination of a four-fold rotational axis and time-inversion symmetry strictly forbids circular-polarizer action. Our symmetry analysis is confirmed by extensive numerical calculations comparing results for perfect electric conductors with those for a free-electron Drude metal with finite damping.
authors.affiliation: Institute of Applied Physics and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany. Johannes.Kaschke@kit.edu
authors.forename: Johannes
authors.initials: J
authors.lastname: Kaschke
authors.forename: Justyna K
authors.initials: JK
authors.lastname: Gansel
authors.forename: Martin
authors.initials: M
authors.lastname: Wegener
mesh_terms: D000042:Absorption; D000465:Algorithms; D003198:Computer Simulation; D004553:Electric Conductivity; D004583:Electrons; D004867:Equipment Design; D007834:Lasers; D008027:Light; D008422:Materials Testing; D008670:Metals; D008859:Microscopy, Polarization / Q000379:methods; D015233:Models, Statistical; D008962:Models, Theoretical; D055095:Optics and Photonics; D013997:Time Factors
chemical_list: D008670:Metals