Sensing Properties Of Surface Plasmon Mim Waveguide Coupled Resonator Cavity Basing On Fano Resonance

Surface Plasmonic Polaritons(SPPs)are a form of collective oscillation on the metal surface produced by the interaction of incident light with free electrons.The electromagnetic field energy can be well localized on the metal surface when the equency of the incident light and the free electrons on the metal surface are the same,so which enhances the interaction between the incident light and the substance.Therefore,using this special optical property can provide a new idea for the design of new optical sensors.As we all known,metal-insulator-metal(MIM)waveguide is a typical surface plasmon waveguide.It can realize the transmission and manipulation of photons under the sub-wavelength scale using SPPs.In this work,the surface plasmons MIM waveguide is used as the sensing structure,and the Fano resonance effect is used as the basis for the sensing.This work explores the transition from a unilaterally coupled resonator waveguide struture to a bilaterally coupled resonator waveguide structure,from a single Fano resonance effect to multiple independent tunable Fano resonance effect.The content of this article is as follows:Firstly,starting from the basic theory of surface plasmons,we explore the excitation methods and application conditions of surface plasmons.Based on this,the mechanism of surface plasmon MIM waveguide coupled the coupling-cavity resonator and Fano resonance principle are explained and studied.A Fano resonant sensing structure of a MIM waveguide coupled cavity with a metal baffle is constructed,and the transmission mechanism of the structure is analyzed by coupled mode theory.In adittion,The waveguide structure is simulated with COMSOL simulation software based on the finite element method to analyze the influence of its structural parameters on the sensing characteristics.It provides a theoretical basis for the design of multiple independent tunable Fano resonance structures.Secondly,the MIM waveguide coupled T-shaped Cavity with a single-baffle optical micro-nano structure is proposed,which can achieve both dual Fano resonance and independent tunability of Fano resonance peaks.Fano resonance is an asymmetric spectral line formed by the destructive interference between the narrow discrete state formed by T-shaped cavity and the wide continuous state formed by the metallic baffle under the near-field coupling.Basing on the coupled mode theory,the generation mechanism of Fano resonance of MIM waveguide coupled T-shaped Cavity with single baffle is studied,and its structural parameters are optimized.Under the condition of ensuring a certain quality factor,the sensitivity of the sensor is greatly improved.This structure can realize the simultaneous modulation of different wave bands.Lastly,in order to further solve the problem of environmental cross-sensitivity,based on the structure of MIM waveguide coupled a single T-shaped Cavity with a single baffle,a MIM waveguide struture of bilateral coupled cavity is proposed.Due to the introduction of a bilateral coupling struture,the original resonance mode is split,and the structure can achieve triple or quadruple Fano resonance effects by increasing or decreasing the number of resonators.By analyzing the influence of the structural parameters of the upper and lower T-shaped Cavity on the Fano resonance peaks,it is found that the Fano resonance peaks generated by the upper and lower T-shaped Cavity do not affect each other,and two Fano resonance peaks can be independently tunable by a single T-shaped Cavity.Using this characteristic,the method of differential sensing is used to extend the refractive index function of multiple Fano resonances.The results show that the use of differential sensing can effectively eliminate the effects of errors caused by ambient temperature and humidity during the detection process,showing the great application potential of multi-Fano resonance in differential sensing.