Currently,many sensing structure models can only sense the refractive index of single variable samples to be measured.In order to achieve high-throughput detection of different samples to be measured and reduce the interference of environmental factors,a variable period subwavelength dielectric grating multilayer composite structure based on wavelength modulation is proposed.Take the double period as an example for analysis.The variable period grating layer is composed of two dielectric gratings,A and B,with different grating periods.The transmission characteristics are analyzed by the finite element method.The TE polarized incident light is incident on the surface of the dielectric grating in a manner perpendicular to the surface of the grating layer.When the phase matching conditions are met in the dielectric grating areas A and B,the variable period subwavelength dielectric grating will form GMR,Providing two double discrete resonance defect peaks with a single narrow band.Because the F-P-like cavity contains a periodic photonic crystal,the photonic band gap will be generated when the light wave propagates to the photonic crystal,providing a wide band continuous state.Under the condition that the phase matching condition is satisfied,the double discrete state resonance defect peak formed in the variable period subwavelength waveguide structure is coupled with the continuous state formed in the F-P-like cavity composed of the periodic photonic crystal multilayer dielectric film,and the double Fano resonance is realized.Then,by exploring the influence of waveguide layer thickness dw and photonic crystal cycle number N on the sensing characteristics,we choose dw=97 nm and N=3 to maximize the FOM value.Finally,the variable period dielectric grating layer is composed of two materials with different dielectric refractive indices,two sensing and detection units can be set in the grating groove part of the dielectric grating areas A and B,and a dual Fano resonance all-dielectric sensing model based on wavelength modulation is established.Different sensing and detection areas are set,and it is found that the dual Fano spectral curve can change with ns1 and ns2 in different sensing and detection areas;the dynamic detection of the refractive index of the sample to be measured is indirectly realized.Therefore,the multivariate detection of different refractive index intervals of the sample to be measured can be realized in the same sensing structure model.The results show that the FOM values of FR1 and FR2 in the sensor detection unit A are 631.53 and 463.7 RIU-1,respectively;in the sensor detection unit B,the FOM is 480.67 and 834.04 RIU-1 respectively.The sensor structure model designed has realized high reflectivity,high FOM value and wide detection range of the sensor structure through structural parameter optimization,which provides a theoretical reference for the dual Fano resonance and has certain research value for the multivariate detection of the sample's refractive index to be measured.
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