Research Of Tunable Fano Resonant Refractive Index Sensor Based On Surface Plasmon Polaritons

An electromagnetic field with a sufficiently high frequency is applied to the interface between the metal and the medium,and a charge density wave formed by the interaction of electrons and photons on the interface is called surface plasmon polaritons(SPPs).When the frequency of the entire collective oscillation of the electrons is consistent with the frequency of the incident light wave,a unique resonance phenomenon will be generated,thus forming a unique electromagnetic mode,which limits the electromagnetic field to the surface of the metal and the medium,and the energy is on both sides of the metal and the medium.It decays exponentially,which is an important way to break through the traditional diffraction limit.Through this approach,it not only solves the problems that have plagued people for many years due to the limited diffraction of the device and cannot be further developed,but also opens the door to the integration of photonic devices for people.The SPPs refractive index sensor based on Metal-Insulator-Metal(MIM)waveguide has attracted wide attention because of its high sensitivity,large quality factor,small size,and easy processing and integration.Recent studies have shown that MIM-based waveguides can produce some novel nonlinear optical effects,such as Fano resonance,electromagnetically induced transparency,and so on.The researchers found that because Fano resonance is extremely sensitive to changes in structural parameters and the refractive index of the medium,Fano resonance has great advantages in the preparation of refractive index sensors.The Fano resonance effect achieved by the MIM waveguide coupled resonant cavity structure is used to design high sensitivity.The refractive index sensor is a very promising approach.The main methods and theories used in this article are Finite Element Method(FEM)and Multimode Interference Coupled Mode Theory(MICMT).The method combines theoretical derivation and actual simulation to study The main work of the research on the transmission characteristics of the MIM waveguide based umbrella resonator refractive index sensor and the MIM waveguide based tunnel resonator refractive index sensor is as follows:1.Designed a refractive index sensor based on the umbrella resonator of the MIM waveguide,and used FEM and MICMT to compare the theoretical and simulated values.The agreement between the two is very high and almost coincides.The refractive index sensor of the umbrella resonator is analyzed.The influence of structural parameters on sensing characteristics.The designed umbrella resonant cavity is not only very sensitive to changes in structural parameters,but also can achieve independent tuning of the resonance peak.After optimizing the structural parameters and changing the filling material,two indicators are used to test the practical application of the umbrella resonator,reached 1600(nm/RIU),and the maximum value of FOM*also reached 193.00.2.Balancing high sensitivity and high quality factor is a key issue in the design of refractive index sensors,so it is very necessary to design a refractive index sensor with moderate quality factor and sensitivity.Based on this,a tunnel-shaped cavity waveguide structure based on MIM waveguide is designed,and the influence of structural parameters g,t,R₁ and R₂ on the sensing performance of the tunnel-shaped cavity structure is studied by FEM.The designed tunnel-shaped resonant cavity can achieve semi-independent tuning in the 700nm-1600nm band,and exhibit linear growth.The maximum sensitivity of the tunnel cavity reaches 2000(nm/RIU),and the maximum value of FOM*also reaches 195.27.