Bistable transmission of nonlinear planar metamaterial with high structural symmetry via trapped-mode excitation S. L. Prosvirnin 1,2 and V. R. Tuz 1,2 1 Institute of Radio Astronomy, National Academy of Sciences of Ukraine 4, Krasnoznamennaya st., Kharkiv 61002, Ukraine; email: prosvirn@rian.kharkov.ua 2 School of Radio Physics, Karazin Kharkiv National University 4, Svobody Square, Kharkiv 61077, Ukraine; email: vladimir.r.tuz@univer.kharkov.ua Abstract We argue the possibility of realization of a polarization insensitive all-optical switching in a planar metamaterial composed of a 4-fold periodic array of two concentric metal rings placed on a substrate of nonlinear material. It is demonstrated that the switching may be achieved between essentially different values of transmission nearly the frequency of the high-quality-factor Fano-shape trapped- mode resonance excitation. 1. Introduction Considerable recent attention has been focussed on the phenomena of optical bistability due to the possi- bility of its practical application to completely optical logic circuits, switches, limiters, optical transistors and diodes. In passive bistable devices, the nonlinear medium is placed inside some optical cavity, and control of operating conditions of the light propagation is provided with light [1]. The issue of the day is to reduce the size of such optical devices, decrease their switching times and the required intensity of light. To do that, photonic crystal microcavities, plasmonic and quantum well structures were proposed to enhance the nonlinear effects as well as to reduce the material volume. In all these cases, the excitation of high-quality-factor resonances in the systems is provided to obtain efficient switching. Exceptionally strong and narrow resonances are also possible to obtain in planar metamaterials designed on the basis of multi-element periodic arrays via engaging trapped-modes [2]. In the regime of quasi-trapped-mode excitation of an actual structure, the field is strongly localized to the structure plane and the resonant transmission and reflection have a large quality factor due to very small radiation of electromagnetic energy in a comparison with stored one. Typically, metamaterials which can bear trapped-modes consist of identical subwavelength metallic in- clusions structured in the form of asymmetrically split rings [2, 3] or split squares [4]. These elements are arranged periodically and placed on a thin dielectric substrate. The characteristic feature of such metamaterials is the dependence of their spectra on the polarization and the angle of incidence of input wave. In [5, 6, 7], the polarization and incidence direction insensitive structures were also proposed. One of such structures consists of a planar array which periodic cell element consists of two concentric rings (double-ring (DR) structure). Remarkably, at the trapped-mode resonance in the DR structure the electromagnetic energy is confined to a very small region between the rings, where the energy density reaches substantially high values. It provides the response of the metamaterial operating in the trapped- mode regime extremely sensitive to the dielectric properties of the substrate. This feature can be used for enhancing optical nonlinearity response in the nanoscaled version of the metamaterial [8]. Metamaterials '2011: The Fifth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics ISBN 978-952-67611-0-7 - 805 - © 2011 Metamorphose-VI