Research On Fano Resonance Sensing Characteristics Based On MDM Waveguide Surface Plasmon

SPPs are electromagnetic waves generated by the coupling of free electrons and incident light waves on a metal surface.SPPs break through the diffraction limit,propagate forward at the metal-dielectric interface,and decay exponentially in a direction perpendicular to the interface.MDM waveguides have a strong ability to restrain SPPs.Optical signals are controlled by SPPs at sub-wavelength dimensions,and the Fano resonance effect generated in the MDM waveguide structure is extremely sensitive to environmental changes.Therefore,it is necessary to deeply explore the design of Fano resonance sensors based on the plasmon of MDM waveguide surface.Based on coupled mode theory and finite element method,the formation mechanism of Fano resonance and the transmission characteristics of SPPs in MDM waveguides are described in detail in this paper.In this paper,three Fano resonance sensing structures are designed based on the surface plasmons of MDM waveguides,which realize single Fano resonance,independently tuned double Fano resonance,and independently tuned multi Fano resonance system design.The main contents are as follows:First of all,based on the structural characteristics of the narrow-spectrum mode generated by the square cavity and the broad-spectrum mode generated by the F-P cavity,a single Fano resonance structure of a MDM waveguide coupled to a square cavity with a bimetal baffle is designed.The interference between discrete and continuous states forms Fano resonance,and the influence of structural parameters on sensing characteristics is explored.Secondly,a double-baffle MDM waveguide is designed to couple two square cavities.The F-P cavity generates a broad-spectrum mode and the two square shaped cavities generate two narrow-spectrum modes that interfere with each other,forming an independently tuned dual Fano resonance.Moreover,independent tuning of dual Fano resonance can be achieved by changing the size of the two square cavities and the filling medium.By optimizing the parameters,a sensing structure with high sensitivity and high FOM value can be obtained.Finally,in order to design an independently tunable multiple Fano resonance structure,a laterally cascaded square cavity was introduced.A double-baffle MDM waveguide coupled laterally cascaded square cavity structure was designed to achieve independently tuned multi-Fano resonance.By adding a disc-shaped gain medium in a square cavity,the sensing performance of the structure is improved,and a double-baffle MDM waveguide with a gain medium coupled with a laterally cascaded square cavity Fano resonant structure is designed.This structure not only can realize the independent tuning of multi-Fano resonance by changing the size of the horizontally cascaded square cavity and the filling medium,but also very sensitive to the change of the refractive index,thereby achieving a multifunctional and high-sensitivity sensing design.