Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators.

Zhaofeng Li,Semih Cakmakyapan,Xiaodong Yang,Stelios Tzortzakis,Bayram Butun,Christina Daskalaki,Ekmel Ozbay

doi:10.1364/oe.22.026572

Abstract

We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices.

Highlights

Before the conceptual work of Fano resonance in 1961 [1], the Lorentzian formula was regarded as the fundamental lineshape of a resonance
We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators
By using a transmission line combined with lumped element model, we are able to fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, and reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance

Summary

Introduction

Before the conceptual work of Fano resonance in 1961 [1], the Lorentzian formula was regarded as the fundamental lineshape of a resonance. The dipole resonator is considered as a bright mode that can be excited by the incident wave, while the quadrupole resonator is considered as a dark mode that cannot be excited by the incident wave directly Another way to create Fano resonances is to introduce symmetry breaking into plasmonic systems. While the CMO model can help us to understand the nature of Fano interference, its parameters do not correspond directly to the properties of the plasmonic structures so that the CMO model can hardly be used in the real design. Another method of lumped circuit elements was proposed to study the response of plasmonic nanostructures [39, 40]. Such “Fano metamaterials” could be exploited for the development of slow light devices

The design of the Fano structures

Experiment results and discussions

Conclusions