Research On Refractive Index Sensing Characteristics Of Mid-infrared Fano Resonant Meta-surface

Fano resonance is a special physical phenomenon in nature.It is formed by the coupling of a discrete state and a continuous state,and has the characteristics of an asymmetric line.Fano resonance can show sharp resonance peaks and significant near-field enhancement,so it has huge potential applications in the fields of optical switching,optical sensing,optical modulation,and nonlinear optics.In recent years,scientists have discovered the phenomenon of Fano resonance in structures such as micro-nano structures and photonic crystals.Afterwards,a large number of Fano resonant optical devices based on metal micro-nano structures have been designed,but the shortcomings of metal itself such as ohmic loss greatly limit the application of metal materials in micro-nano photonics.Later,it was discovered that some all-dielectric materials were used to solve these problems in metal structures,such as materials such as germanium,silicon and gallium arsenide with high refractive index.This provides a new way for the development of ultra-integrated ultra-precision micro-nano optical devices.Based on this,this paper proposes an all-dielectric micro-nano structure refractive index sensor designed on the germanium surface,and the Fano resonance with high quality factor is obtained by optimizing the structural parameters.In addition,this article also proposes a method to solve the loss of metal itself,design the metal micro-nano structure on the photonic crystal,and use the coupling between the Fano resonance generated by the photonic crystal and the Fano resonance generated by the surface structure to enhance the quality factor of the resonance peak.The main research results of this paper are as follows:(1)A double split ring structure is designed on the germanium surface of the whole dielectric to achieve Fano resonance with high quality factor and high sensitivity.First,we break the symmetry of the structure by changing the offset of the middle rod of the structure and excite the Fano resonance.By simulating the magnetic field distribution on the surface of the structure and comparing the reflection spectra before and after breaking the symmetry,the analysis reveals the physical mechanism of the Fano resonance in the structure.At the same time,we apply the structure sensor in the field of refractive index optical sensing.It is the sensor performance ratio of the same kind of all-dielectric in recent years,and the sensing performance has been greatly improved.The sensitivity can reach 662nm/RIU,and the FOM can reach 262.(2)The cross-hair structure is designed on the germanium surface of the whole medium,which is similar to the double split ring structure,and the resonance wave peak is also excited by breaking the symmetry of the structure.And the influence of the offset of the middle rod and the period of the unit structure on the structure sensitivity and quality factor is simulated and analyzed.The reflection spectrum and surface magnetic field density distribution of the structure are calculated by the finite element method,as well as the change of the magnetic field density when the middle rod is offset.Through structural optimization,the maximum sensitivity of2100nm/RIU and the maximum quality factor of 31.8 are obtained.And the refractive index sensing performance of the sensor is verified through experiments.A cross-hair micro-nano structure was prepared on a germanium film based on zinc selenide,and the structure was combined with a microfluidic device.The structure was verified by changing the refractive index of the solution in the structure environment and observing the change in the transmission spectrum of the structure.The refractive index sensing characteristics.(3)The metal Ag rod-concentric ring disk nanostructure is designed on the photonic crystal,and the physical mechanism of the Fano resonance caused by this structure is theoretically studied.This structure can generate multiple sharp Fano resonances in the photonic crystal and surface metal structure,and multiple Fano couplings can excite peaks with better sensing performance.Simultaneously,the influence of the thickness of the metallic Ag film on the surface of the structure and the number of photonic crystal periodic layers on the sensing performance of the structure was also simulated and discussed.Finally,the structure is applied to refractive index sensing,and the maximum quality factor can reach 8900.