Study On Fano Resonance Sensing Properties Of Multilayer Thin Films Based On Sub-wavelength Dielectric Grating

Due to the unique optical properties of sub-wavelength dielectric gratings,the combination of dielectric film optics,waveguide optics and diffractive optics can be used to design sub-wavelength optical components.It has the advantages of high figure of merit(FOM)and structural diversity,and has great application prospects in the field of optical sensor design.Based on the research on the structural properties of sub-wavelength dielectric gratings and the formation mechanism of Fano resonance,this paper combines multilayer dielectric films with sub-wavelength dielectric gratings,and a sub-wavelength dielectric grating sensing structure based on Fano resonance is designed.And then,the resonance mode and sensing properties of the sensing structure model are discussed by finite element method(FEM),so as to realize the gradual optimization and improvement of the multilayer thin film sensing structure based on the sub-wavelength dielectric grating.The main research contents of this paper include:Firstly,based on the diffraction properties of the sub-wavelength dielectric gratings and the optical transmission properties of surface plasmon polartions(SPPs),a composite structure of sub-wavelength dielectric grating / metal Ag thin film /periodical photonic crystal is designed.The Fano resonance formation mechanism and optical transmission properties of the sensing structure model are analyzed in detail.The relationship between the structural parameters and the Fano resonance spectral curve is explored,and the sensor structure model is optimized,which provides theoretical guidance for the research of multilayer thin film sensing structures based on sub-wavelength dielectric gratings.Secondly,based on the resonance properties of the sub-wavelength waveguide grating and the photon local properties of the periodic photonic crystal,a composite structure of sub-wavelength waveguide grating and all-dielectric multilayer film based on angle modulation is designed.The Fano resonance spectral curve with high reflectivity and high FOM value is obtained by using the optical properties of all-dielectric materials.And then,by changing the incident mode and structural parameters,the limitation of the propagation conditions of the sub-wavelength waveguide grating is broken,and a composite structure of sub-wavelength waveguide grating and all-dielectric multilayer film based on wavelength modulation is designed.Thereby,the dynamic detection of the refractive index of samples to be measured is further realized in the wavelength range,and the detection and analysis method is expanded.Finally,a composite structure of variable period subwavelength waveguide grating and all-dielectric multilayer film based on wavelength modulation is designed.By using the structural properties of the variable period sub-wavelength waveguide grating,the guided mode resonance(GMR)can be formed in different wavelength ranges and double discrete defect peaks can be provided,thereby realizing double Fano resonance spectral curve with high FOM value and high reflectivity.And then,according to the weak modulation condition of the sub-wavelength waveguide grating,the dual sensing detection area is set.The sensing properties are analyzed by establishing a sensing model based on double Fano resonance.Therefore,the multivariate detection of samples to be measured with different refractive index range is realized and the sensing detection range is enlarged.