Sharp Fano resonances in THz metamaterials

Ranjan Singh,Martin Koch,Weili Zhang,Ibraheem A I Al-Naib

doi:10.1364/oe.19.006312

Abstract

We report on the occurrence of sharp Fano resonances in planar terahertz metamaterials by introducing a weak asymmetry in a two gap split ring resonator. As the structural symmetry of the metamaterial is broken a Fano resonance evolves in the low-frequency flank of the symmetric fundamental dipole mode resonance. This Fano resonance can have much higher Q factors than that known from single gap split ring resonators. Supporting simulations indicate a Q factor of 50 for lowest degree of asymmetry. The Q factor decreases exponentially with increasing asymmetry. Hence, minute structural variations allow for a tuning of the Fano resonance. Such sharp resonances could be exploited for biochemical sensing. Besides, the strong current oscillations excited at the Fano resonance frequency could lead to the design of novel terahertz narrow band emitters.

Highlights

Metamaterials is a flourishing field of science and engineering that exploits the exotic optical properties of subwavelength metallic structures to manipulate light at ultra small length scales
We report on the occurrence of sharp Fano resonances in planar terahertz metamaterials by introducing a weak asymmetry in a two gap split ring resonator
We report on sharp Fano resonances arising from a gentle symmetry breaking in a two gap terahertz split ring resonators (SRRs) structure

Summary

Introduction

Metamaterials is a flourishing field of science and engineering that exploits the exotic optical properties of subwavelength metallic structures to manipulate light at ultra small length scales. Planar metamaterials are optically thin structures having modest quality factors since they do not have an inner resonating volume for high energy confinement Their resonating units are usually strongly coupled to free space which in turn causes high radiation losses. With increasing degree of structural asymmetry between the two arms of the SRR we observe an increase in the strength of the asymmetric resonance but a gradual decline in its Q factor Such “Fano metamaterials” can have applications in diverse areas ranging from micro photonics and biochemical sensing to cavity quantum electrodynamics since their ability to concentrate electromagnetic fields in an extremely small spatial region forms the key to strong terahertz radiation matter interaction. The sharp resonance could be exploited for developing slow light devices by invoking an electromagnetically induced transparency (EIT)-like response in the metamaterials [42,43,44,45,46,47,48,49]

Experiment

Measurement and Simulation

Discussion

Findings

Conclusion