Formation Laws of Direction of Fano Line-Shape in a Ring MIM Plasmonic Waveguide Side-Coupled with a Rectangular Resonator and Nano-Sensing Analysis of Multiple Fano Resonances

Dayong Zhang,Li Cheng,Zuochun Shen

doi:10.3390/cryst11070819

Dayong Zhang, Li Cheng + Show 1 more

Open Access

https://doi.org/10.3390/cryst11070819

Copy DOI

Abstract

Plasmonic MIM (metal-insulator-metal) waveguides based on Fano resonance have been widely researched. However, the regulation of the direction of the line shape of Fano resonance is rarely mentioned. In order to study the regulation of the direction of the Fano line-shape, a Fano resonant plasmonic system, which consists of a MIM waveguide coupled with a ring resonator and a rectangle resonator, is proposed and investigated numerically via FEM (finite element method). We find the influencing factors and formation laws of the ‘direction’ of the Fano line-shape, and the optimal condition for the generation of multiple Fano resonances; and the application in refractive index sensing is also well studied. The conclusions can provide a clear theoretical reference for the regulation of the direction of the line shape of Fano resonance and the generation of multi Fano resonances in the designs of plasmonic nanodevices.

Highlights

Surface plasmon polaritons (SPPs) are transverse magnetic (TM)-polarized surface waves, which originate from interactions between incident photons and free electrons on metal surface and propagate along metal-dielectric interface
In the traditional middle infrared waveguide sensor, the diffraction limit appears when the waveguide size is gradually reduced to the wavelength order, and the wave propagation distance decreases abruptly, which makes greatly reduces the performance of the device
The black solid line is the result of the coupling between the continuum and the located state; and the three sharp asymmetric line-shapes in the black solid line are the results of Fano resonance, marked as FR1, FR2, and FR3

Summary

Introduction

Surface plasmon polaritons (SPPs) are transverse magnetic (TM)-polarized surface waves, which originate from interactions between incident photons and free electrons on metal (like silver and gold) surface and propagate along metal-dielectric interface. Different from the traditional middle infrared waveguide sensor, the plasmonic MIM waveguides can overcome the diffraction limit and can limit the light in the sub-wavelength spatial dimension, as a result, the device is easy to be miniaturized. The plasmonic MIM waveguides combined with the Fano resonance effect are widely researched. The research on plasmonic MIM waveguides based on Fano resonance mainly focuses on the creation of Fano resonance by resonators with different geometric shapes [7,8,9,10,11,12,13,14], the influence of the different geometric parameters of these resonators on. The the proposed structure for multiple Fano resonances are analyzed and selected to study where km and kd are kd2 = εd k02 − β 2 and km2 = εm k02 − β 2 , with εd and εm defined as dielectric the refractive index sensing. The effective refractive index of the plasmonic waveguide is expressed as Neff

Materials andbetween

Schematic

Analysis of the Formation Laws of the ‘Direction’ of the Fano Line-Shape

Nano-Sensing Analysis

Conclusions investigate find influencing factors and formation laws direction