Study On Controllable Fano Resonance Of MIM Waveguide Coupling Defect Resonant Cavity System

With the rapid development of science and technology,although light as a transmission carrier has made tremendous progress in information transmission,traditional photonic devices,due to the existence of diffraction limit,make it unable to meet the current high speed of information Transmission needs.Surface plasmon polaritons(SPPs)are the electromagnetic wave modes spread along the metal surface.They arise from the coupling of incident photons and free electrons on the surface of metals.The electric field intensity of SPPs decays exponentially in the direction perpendicular to the metal-dielectric interface.SPPs break the traditional optical diffraction limit and can realize the transmission and processing of optical information at a nanometer scale.Specifically,metal–insulator–metal(MIM)waveguide,which is one of the SPPs-based waveguides and has the merits of strong local field enhancement characteristics,suitable propagation length,and easy integration,and has potential application value in highly integrated photonic circuits.There are many optical devices that have been studied,such as plasmonic sensors,filters,and splitters.These devices are based on MIM waveguides and made up of waveguides and resonators.Special optical effects can be produced by MIM waveguide coupled resonators,such as Fano resonance and in some cases,electromagnetically induced transparency(EIT).Fano resonance can be considered as an analogy of EIT.Plasmonic systems based on Fano resonance are likely to be highly sensitive sensors because of its sharp and asymmetrical line shape,owing to which,its transmittance spectrum can be rapidly reduced from the peak to the trough.The full wide half magnitude(FWHM)of this transmission spectrum is relatively narrow and can be easily identified and tracked;thus,greatly improving the sensing resolution.A large number of refractive-index sensor structures based on Fano resonance have been reported.Based on Coupled Mode Theory(CMT)and Finite element method(FEM),this paper studies the Fano resonance phenomenon in the MIM waveguide coupling defect resonator structure,and three kinds of high-sensitivity refractive index sensors based on Fano resonance effect are designed,the main work of this paper is as follows:Herein,the design for a tunable plasmonic refractive index nanosensor is presented.The sensor is composed of a metal–insulator–metal waveguide with a baffle and a circular split-ring resonator cavity.Analysis of transmission characteristics of the sensor structures was performed using the finite element method,and the influence of the structure parameters on the sensing characteristics of the sensor is studied in detail.The calculation results show that the structure can realize dual Fano resonance,and the structural parameters of the sensor have different effects on Fano resonance.The peak position and the line shape of the resonance can be adjusted by altering the sensitive parameters.The maximum value of structural sensitivity was found to be 1114.3 nm/RIU,with a figure of merit of 55.71.A plasma refractive index nanosensor based on Fano resonance is designed,which is composed of the metal-insulator-metal waveguide with a stub coupled with a split-square resonator.Analysis of transmission characteristics of the sensor structures was performed using the finite element method,and the influence of the structure parameters on the sensing characteristics of the sensor is studied.The calculated results show that the structure can excite the Fano resonance,and the resonance peak wavelength and linetype can be adjusted by changing the key parameters.By adjusting the structural parameters,the sensitivity of the structure is up to 1125.7 nm/RIU and the Fom is 30.01.The structure of a coupled split ring resonator with stub MIM waveguide is designed.The effects of structural parameters such as the center radius of the split ring resonator and the coupling spacing between the split ring resonators on the Fano resonance line shape are studied.Finally,the refractive index sensing characteristics of the coupled structure were studied to optimize the structural parameters.The sensitivity of the refractive index of this structure reached 1071.4 nm / RIU,and the corresponding maximum FOM was 14.29.In this paper,three kinds of MIM waveguide coupling defect cavity structures are designed,and the light propagation characteristics and refractive index sensing characteristics of different structures are analyzed.The above work can provide a new reference for the on-chip plasma nano-refractive index sensor.