title: On the origin of pure optical rotation in twisted-cross metamaterials.
abstract: We present an experimental and computational study of the response of twisted-cross metamaterials that provide near dispersionless optical rotation across a broad band of frequencies from 19 GHz to 37 GHz. We compare two distinct geometries: firstly, a bilayer structure comprised of arrays of metallic crosses where the crosses in the second layer are twisted about the layer normal; and secondly where the second layer is replaced by the complementary to the original, i.e. an array of cross-shaped holes. Through numerical modelling we determine the origin of rotatory effects in these two structures. In both, pure optical rotation occurs in a frequency band between two transmission minima, where alignment of electric and magnetic dipole moments occurs. In the cross/cross metamaterial, the transmission minima occur at the symmetric and antisymmetric resonances of the coupled crosses. By contrast, in the cross/complementary-cross structure the transmission minima are associated with the dipole and quadrupole modes of the cross, the frequencies of which appear intrinsic to the cross layer alone. Hence the bandwidth of optical rotation is found to be relatively independent of layer separation.
authors.affiliation: Electromagnetic Materials Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Barr
authors.affiliation: Wave Phenomena Group, Department of Electronics Engineering, Universitat Politècnica de Valéncia, Camino de Vera S/N. (Edificio 7F1), ES-46022 Valencia, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Díaz-Rubio
authors.affiliation: Electromagnetic Materials Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom.
authors.forename: Ben
authors.initials: B
authors.lastname: Tremain
authors.affiliation: Wave Phenomena Group, Department of Electronics Engineering, Universitat Politècnica de Valéncia, Camino de Vera S/N. (Edificio 7F1), ES-46022 Valencia, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Carbonell
authors.affiliation: Wave Phenomena Group, Department of Electronics Engineering, Universitat Politècnica de Valéncia, Camino de Vera S/N. (Edificio 7F1), ES-46022 Valencia, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Sánchez-Dehesa
authors.affiliation: Electromagnetic Materials Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom.
authors.forename: Euan
authors.initials: E
authors.lastname: Hendry
authors.affiliation: Electromagnetic Materials Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom.
authors.forename: Alastair P
authors.initials: AP
authors.lastname: Hibbins