Studv On Multimode Excitation And Sensing Characteristics In All-dielectric Metasurfaces

Scientific and effective regulation of electromagnetic wave has important research significance in the fields of communication,national defense,medical treatment,industry and so on.As one of the "top ten technological breakthroughs of the first decade of the century,"metasurfaces have greatly enhanced and expanded electromagnetic modulation capabilities and have been applied to electromagnetic cloaking,metalenses,negative refraction,sensing,and many other fields.Among them,sensing is the key step to provide information for biology and chemistry,and the introduction of a new method with high sensitivity,robustness and low cost has been the focus of recent research.Due to low optical loss and strong light matter interaction,dielectric metasurface shows some unique optical properties,including sharp resonance,strong near-field enhancement and strong ability to support magnetic mode.It has become a powerful platform for new optical sensors.Based on the finite difference time domain method,the excitation and regulation mechanism of multiple Fano resonances in different dielectric metasurfaces are studied and applied to refractive index sensors.The main research results are as follows:(1)A dielectric metasurface based on "square holes" is designed.By introducing asymmetric parameters,multiple Fano resonances are successfully excited in the near-infrared band.Among them,the current distribution at the resonance wavelength exhibits the characteristics of magnetic dipole(MD)and toroidal dipole(TD)with strong field-binding capability.The structure is flexible and adjustable in geometric parameters and has good experimental feasibility.The highest sensitivity and FOM values are 293.75 nm/RIU and 700 RIU-1,respectively,when it is applied to refractive index sensing.(2)Further,the design scheme of "square hole" is changed to"semicircular hole",and the resonant wavelength is successfully transferred to 1310nm and 1550nm.At the same time,through the destructive interference between the electric dipole(ED)and TD in the far field,a special "Anapole" mode is realized at 1371.3 nm,and the field localization ability is further enhanced.The scheme can simultaneously support MD,EQ(electric quadrupole),TD and other Mie scattering resonances,with richer modes and better experimental results.(3)A dielectric metasurface composed of Si nanorods is designed in a symmetrical configuration,and the toroidal resonance of ultra-high Q factor is realized.With the help of graphene materials,the reflectivity is tuned and the absorption spectrum exhibits an extremely narrow Lorentzian line pattern.At the same time,three different substrate etching schemes are innovatively proposed to improve the sensitivity of sensing,thus effectively enhancing the area of interaction between light and matter.The designed optical refractive index sensor has a sensitivity of up to 500.75 nm/RIU and a maximum FOM value of 3013.33 RIU-1,which provides excellent sensing performance.In addition,they also show advantages over plasma counterparts,such as CMOS compatible manufacturing process and low resonance heat loss.These unique characteristics promote the development of cutting-edge sensing technology in new applications.The all-dielectric metasurface structure designed in this paper is simple and easy to integrate,which provides a new solution for the study of high-performance optical refractive index sensors.