Nanowire Dimer Metamaterial: Design, Fabrication and Optical Characterization

In this work we report on the electromagnetic resonances excited in a planar metamaterial consisting of pairs of gold bars(dimers) arrayed on a dielectric substrate. In the case of equal bar lengths, bright resonance modes can be easily excited, which couple strongly to free space and posses a low Q-factor. The introduction of bar length asymmetry induces the excitation of the so-called dark modes which couple very weakly to free space and show high Q-factors. The interaction of the dark and bright resonant modes results in a Fano type profile of the resonance. With increasing length asymmetry, coupling of the dark modes to free space is increased, resulting in a lowered Q-factor. We discuss the dependence of both the dark and bright modes on the dimer geometry and refractive index of the metamaterial environment, in order to optimize the structure for a potential application as an optical sensor. Effective material parameters were obtained from spectroscopic ellipsometry study of the metamaterial on a glass substrate and their physical meaning and applicability are discussed. Experimental results show good agreement with simulation.