Design And Research Of MIM Waveguide Coupled Resonator System Based On Fano Resonance

Under the background of information age,traditional optoelectronic devices with large volume,large loss and poor stability have gradually failed to meet people’s needs for development.Surface plasmon polaritons(SPPs)are electromagnetic surface waves generated by the interaction between an external light field and free electrons in metal,which can reach the maximum field intensity on the surface and decay exponentially along the direction perpendicular to the interface.Because SPPs can break through the traditional optical diffraction limit and control the optical signal in the subwavelength structure,the optical devices based on SPPs have the characteristics of nanoscale integration,high stability and low loss.Therefore,more and more researchers devote themselves to the study of surface plasmon polaritons.The metal-insulator-metal(MIM)waveguide has the ability of transmitting SPPs.Based on the characteristics of the MIM waveguide such as simple structure,easy excitation and strong insulator ability,the MIM waveguide gradually becomes the most dominant carrier in the development of high integration optical devices application.Based on the MIM waveguide structure,many coupled resonator systems based on SPPs have been designed and successfully applied in the fields of filters,couplers,reflectors,optical switches and biosensors.In this study,three MIM waveguide coupled resonator sensing structures are designed and analyzed based on the finite element analysis method,and they are well applied in the field of biosensor.The sensor system is based on the Fano resonance phenomenon.The linear shape of the Fano resonance and the detection performance of the sensor can be adjusted by changing the structural parameters of the resonant cavity and the waveguide.COMSOL Multiphysics 5.4a software was used for modeling and simulation,and finally the sensing performance of the proposed structure was obtained.The specific work content and results are as follows:(1)A coupling system with a MIM waveguide and a circular ring containing a disk-shaped cavity is studied.The influence of the disk-shaped cavity on the Fano resonance phenomenon is analyzed by comparison and the influence of the geometrical parameters of the structure on the transmission characteristics of the system is studied.The maximum sensitivity and the figure of merit(FOM)of the sensor system were optimized to reach 2240nm/RIU and 62.5,respectively,and the sensitivity of 1.186 nm/℃ can be achieved when applied to the temperature sensing field.(2)A sensing system consisting of a circular ring containing a rectangular cavity and a MIM waveguide was developed.The phenomenon of double Fano resonance generated by the system is studied,and the causes and influencing factors are analyzed.By changing the structural parameters of the system,it is found that the dual Fano formants can be tuned independently,and the spectra can be regulated in different frequency bands.Finally,the system can achieve the maximum sensitivity of 2300 nm/RIU and 1440 nm/RIU,which can be applied to the detection of electrolyte concentration in human blood,and can achieve the sensitivity of 3.2 nm·L/g and 3.25 nm·L/g sodium potassium ion concentration.(3)A simple nanostructure consisting of a U-Shaped resonator and an MIM waveguide with two rectangular baffles is propounded.The effects of different structures of MIM waveguides on the transmission characteristics of the system are studied.By changing the geometrical parameters of the structure,the reasons for the formation of Fano resonance and the key factors affecting the wide continuum state and narrow discrete state are explained.The best sensitivity of 2020 nm/RIU and the figure of merit of 53.16 can be achieved by applying the designed compact structure to the field of refractive index sensor.