Tunable and nonlinear fishnet metamaterials based on liquid crystal infiltration Sergey Kruk a , Alexander Minovich a , James Farnell a , Ian McKerracher b , Fouad Karouta c , Jie Tian c , David A. Powell a , Ilya V. Shadrivov a , Hark Hoe Tan b , Chennupati Jagadish b , Dragomir N. Neshev* a and Yuri S. Kivshar a a Nonlinear Physics Centre, Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia; b Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia; c Australian National Fabrication Facility ACT Node, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia ABSTRACT We demonstrate the use of liquid crystal infiltration of fishnet structures for the realization of highly tunable and nonlinear optical metamaterials. We show that fishnet metamaterials infiltrated with nematic liquid crystals can exhibit strong nonlinear response at moderate laser powers. We also show that this nonlinear response arises due to the molecular orientation of the liquid crystal molecules and can be therefore be fine-tuned with an electric field, opening new opportunities for electrically tunable nonlinear metamaterials. Keywords: Metamaterials, fishnet metamaterials, liquid crystals nonlinearity 1. INTRODUCTION Optical metamaterials are artificially engineered materials, structured at the nanoscale that exhibit properties unknown in nature, including magnetism at optical frequencies, negative refractive index, perfect absorption, giant circular dichroism and ultra-high sensitivity to light intensity. As such metamaterials have created a new paradigm in science with applications in ultrahigh-resolution imaging systems, compact polarization optics and invisibility cloaking devices [1, 2]. The main reason behind this unprecedented control over light properties is the ability for independent control over the electric permittivity and the magnetic permeability of the material. While a large amount of work has been undertaken to understand and design the linear properties of metamaterials, the possibility for engineering of the nonlinear properties of metamaterials remains largely unexplored. For example, in metamaterials with pronounced magnetic resonances one can enable nonlinear response of the magnetic polarizability of the material. As such both the electric and magnetic nonlinearity can be enhanced simultaneously, thus opening novel possibilities for the realization of metamaterials that are ultra-sensitive to light. Indeed, different metamaterial structures have been utilized as nonlinear elements. The generation of second and third harmonic has been demonstrated by several groups [3-7], however the conversion efficiencies remain extremely small as the harmonic generation is mostly due to the surfaces. The nonlinear modification of the metamaterials has also been studied by pump-probe techniques [8-10] where a high power beam is used to induce modulation of a weak probe beam. From an application perspective however, the biggest advantage of nonlinearity enhancement in metamaterials can arise from nonlinear self-action effects, where weak beams can induce changes in the materials resulting in self-phase modulation of the beam itself. Enhancement of nonlinear self-action in metamaterial structures has been studied by coupling metamaterials to highly nonlinear substances, such as carbon nanotubes [11] or even the nonlinearity of metal itself [12, 13]. However, in all reports to date such nonlinear self-action has been only tested in plasmonic type metamaterials, which do not support magnetic type resonances. Therefore, in this work we aimed at demonstrating magnetic type nonlinearities in optical metamaterials with magnetic type resonances. Invited Paper Metamaterials: Fundamentals and Applications V, edited by Allan D. Boardman, Nader Engheta, Mikhail A. Noginov, Nikolay I. Zheludev, Proc. of SPIE Vol. 8455, 84552O © 2012 SPIE · CCC code: 0277-786/12/$18 · doi: 10.1117/12.931309 Proc. of SPIE Vol. 8455 84552O-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/27/2013 Terms of Use: http://spiedl.org/terms