Giant gyrotropy in bi-layered chiral structures

We show that a layered structure consisting of two identical planar metal patterns can show exceptionally strong resonant gyrotropy if one pattern is twisted with respect to the other thus creating a 3D-chiral object. This effect is analogous to the gyrotropy of bulk media comprised of chiral molecules was and was first theoretically analyzed in [Appl. Phys. Lett. 78, 498 (2001)]. Using helicoidally arranged planar metal rosettes of 4-fold rotational symmetry we achieved enantiomerically sensitive polarization plane rotation (optical activity) of about 30 degrees and circular dichroism in the microwave part of the spectrum. The ability to create gyrotropic structures utilizing planar technology provides opportunities for manufacturing artificial gyrotropic materials, which can be use to manipulate the polarization state of radiation in the optical and microwave ranges. The range of possible applications of such structures includes computer displays and various opto-electronic devices. Its exceptionally strong gyrotropy can also be used for developing so-called negative refractive-index media wherein simultaneous electric and magnetic resonances at optical frequencies are needed to achieve negative refraction. Using appropriately scaled subwavelength nano-structures we expect to confirm this strong gyrotropy in the optical part of the spectrum