Research On Resonance And Sensitivity Improvement Of Surface Plasmons Sensor System

Surface plasmons(SP)can form localized enhanced fields near the interface of metal and dielectric,overcoming the traditional diffraction limit,and they have important applications in the field of optical sensing.The research topic of this paper is to utilize graphene patterning and Metal-Insulator-Metal(MIM)waveguide structures to excite SP and induce resonances in sensing systems,thereby improving their sensitivity.The specific research contents are as follows.(1)Firstly,this paper proposes a terahertz tunable sensor based on SP resonance,composed of a metal thin film and elliptical defect-shaped graphene.The mechanisms behind the formation of three resonances are analyzed using SP technology combined with coupling theory.This research analyzes the influence of graphene’s structural parameters,Fermi energy level,and relaxation time on the transmission spectrum.The optimal structure of the sensor exhibits transmittance values of 0.051 for Dip I,0.541 for Peak I,and 0.220 for Peak II.The highest sensitivity,figure of merit,and quality factor reach 1.8THz/RIU,9.091,and 40.606,respectively.By adjusting the graphene’s conductivity,the refractive index can be modified,enabling dynamic tuning of the sensor’s performance.(2)Secondly,the paper investigates an SP sensor based on a Y-shaped MIM waveguide structure and analyzes the influence of the resonant cavity on the sensing spectrum.The sensitivity of the Y-shaped symmetrical structure is determined to be 750nm/RIU.By setting the Y-shaped branch length at 120 nm,dual Fano resonances can be achieved,leading to a sensitivity of 1000 nm/RIU.Furthermore,the addition of Ag nanoparticles in the Y-shaped cavity enhances the Fano resonance,resulting in a sensitivity improvement of up to 1160 nm/RIU.The research results demonstrate that the resonance wavelength of Dip II in the sensor linearly varies with the concentration of sucrose solution,enabling the detection of different concentrations of sucrose solutions.(3)Lastly,the paper designs an SP-based Fano resonance fiber sensor.This study utilizes the wavelength shift of Fano resonance caused by changes in refractive index to achieve sensing detection.The sensitivity of the three optimized fiber sensors proposed in this study reaches 750 nm/RIU,1500 nm/RIU,and 1725 nm/RIU,respectively.The optimal structure of the sensor forms three Lorentz resonances in the total electromagnetic energy at 1170 nm,1896 nm,and 2541 nm,with respective Full-Width at Half-Maximum(FWHM)values of 23 nm,25 nm,and 47 nm,and 24 nm,26 nm,and 46 nm.The highest sensitivity reaches 1770 nm/RIU.When the fiber sensor is used for glucose concentration detection,the FWHM of Dip III ranges from 42.6 nm to 44.0 nm.The SP sensor structures proposed in this paper are compact,reliable,and highly sensitive.This research provides new design ideas for the development of sensors based on metamaterials and MIM structures in interdisciplinary fields.