Study On Plasma Sensor Based On Fano Resonance

Surface plasmon is a collective charge oscillation existing at the interface between conductor and dielectric.it is limited to propagate along the metal-dielectric interface and attenuates exponentially along the direction perpendicular to the interface.Because the surface plasmon can overcome the diffraction limit of traditional optics,it is possible for researchers to manipulate optics on the nanometer scale,so it has received extensive attention in the research of optical devices.As the carrier of surface plasmon,MIM waveguide is considered as the most promising candidate for the development of highly integrated optical devices because of its strong local field enhancement characteristics and easy fabrication.Based on MIM waveguides,a large number of sub-wavelength optical devices,such as optical switches,nanosensors,beam splitters and modulators,have been developed and designed.Fano resonance caused by the interference between discrete state and continuous state is a special optical effect in SPP waveguide system.Because of its sharp,asymmetric spectrum and entrance enhancement,it has been widely used in sensors,filters and nonlinear processes.In addition,with the development of highly integrated photonic circuits,multi-Fano resonance has attracted more and more attention because of its advantages in enhanced biochemical sensing,polychromatic spectra and broadband nonlinear processes.More and more structures that induce multiple Fano resonance have been proposed and applied to nanosensors,but most studies can not have both multiple Fano resonance and high sensing performance.In this paper,based on surface plasmon polaritons and Fano resonance,based on MIM waveguide and Drude dispersion model,the number,cause of formation,tunability and sensing performance of Fano peaks of plasma sensor are studied by finite element method.The main work of this paper is as follows:1.Starting from the propagation of surface plasmon on metal surface,the wave equation and dispersion relation of SPP are discussed,the dispersion model of metal-Drude model is briefly described,and the propagation of SPPs in MIM waveguide and several common excitation modes are studied.Then we explain the basic principle of Fano resonance through the two-oscillator model,and analyze in detail several common realization modes of Fano resonance through structural examples.Finally,the numerical simulation methods commonly used in the study of surface plasmons are introduced,with emphasis on the finite element method and the finite-difference time-domain method.2.A plasma sensor based on ring cavity is proposed.The narrow discrete spectrum is generated by the ring cavity,and the wide continuous spectrum is generated by the MIM waveguide inserted into the baffle.The coupling of the two provides two Fano peaks.By adjusting the structure parameters,it is found that the resonant wavelengths of the two Fano peaks also change,which proves that the structure is adjustable.Finally,the structure can be used in refractive index sensor with a sensitivity of 1550 nm/RIU,and a FOM?6.4 × 103.3.Two improved plasma sensors based on ring cavity are proposed.One is that four tunable Fano resonant peaks are generated through the coupling between the discrete state generated by the square cavity(RCSC),through RCSC in the ring cavity and the continuous state generated by the MIM waveguide with a baffle.The structure is used for refractive index sensor and can reach the highest FOM value of 1.39 × 104.The other is the three tunable Fano peaks produced by inserting a double baffle(DBRC),into the ring cavity,which is formed by the interaction between the induced narrow discrete DBRC and the induced continuous spectrum MIM waveguide inserted into the baffle.The structure is used in the refractive index sensor and the maximum FOM value of 1.32 × 104 is achieved.4.A plasma sensor based on notched ring cavity is proposed.The structure consists of left and right MIM waveguides and a rectangular cavity(CSRRTC)of a directly connected notched ring resonator.Five high transmittance Fano peaks are generated due to the interference between different modes of the rectangular cavity and the notched ring cavity.The structure is applied to the sensor,and the highest sensitivity of 1450nm/RIU and the maximum value of FOM of 1.36×105 are achieved.This structure has better performance than most similar structures.It is believed that this structure can promote the development of highly integrated photonics and support the substantive application of nano-sensors.