Study On Light Field Modulation And Application Based On All-dielectric Metasurfaces

Toroidal resonance increases the field limitation by limiting the electromagnetic field in a small ring region,originally proposed by Zel ’dovich in 1957.The proposed Toroidal dipole explains the parity violation of the weak interaction force.Because of its unique electromagnetic properties,the ring dipole attracts a lot of research.However,because the coupling between Toroidal dipole resonance and the incident electromagnetic wave is weak,it is usually masked by stronger electric and magnetic dipoles,which presents a challenge for the detection and application of Toroidal dipole resonance.Fortunately,the introduction of metasurfaces provides an effective way for the research and application of Toroidal dipoles.Although the elements that make up the metasurfaces can be either metal or dielectric materials,the latter is increasingly receiving more attention because of its advantages,as dielectric materials do not suffer ohmic losses when interacting with external excitation fields,while showing a very rich ability to combine exploitable properties,especially when metasurfaces is high refractive index materials.In this thesis,the excitation and regulation of Toroidal dipoles are studied by using all-dielectric metasurfaces.All-dielectric metasurfaces are widely studied for their advantages of simple structure,low loss and low cost.The Toroidal dipole resonance excited in the all-dielectric Toroidal metasurfaces can be widely used in sensors and other devices because of its high Q value due to its radiation-free properties and the presence of enhanced local fields in dielectric resonators.Moreover,the all-dielectric metasurfaces can be applied to a variety of optical devices because of its flexible and adjustable geometry and compatibility with other active materials,so the electromagnetic response to metasurfaces can be dynamically modulated in multiple dimensions.The main structure of this thesis is as follows;The first chapter is the introduction.The development of metamaterials and metasurfaces,their differences and the comparison between their advantages and disadvantages are introduced.Metamaterials were first proposed as negative index metamaterials to explain the negative refraction phenomenon in nature,and then they were further studied and developed.In this chapter,the principle of negative refractive index is elaborated,which is easy for us to have a more specific understanding of the physical principle of artificial design of metamaterials.The three-dimensional(3D)structure of metamaterials has encountered a bottleneck due to the limitation of preparation technology,and then the two-dimensional counterpart of metamaterials,metasurfaces,has gradually become a new research hotspot.The advantages of metasurfaces and its great prospects for application are described in detail in the article section.Then,the main object of this thesis is proposed,namely Toroidal dipole resonance.The development of Toroidal dipoles and the research of Toroidal dipoles on which metasurfaces can be used as an effective ideal platform to excite strong resonance are described in detail in this section.The second chapter mainly introduces the theoretical basis of all-dielectric metasurfaces.Based on the understanding of metasurfaces and Toroidal dipole in Chapter1,it is considered that the all-dielectric metasurfaces has a strong advantage in preparation and application compared with metal metasurfaces.Therefore,the development of alldielectric metasurfaces and the development of all-dielectric metasurface that excites Toroidal dipoles in all-dielectric metasurfaces are described in detail,and the excellent research results in recent years are listed respectively.Then,in order to more accurately describe the specific contribution of excited multidipoles to the scattered field in metasurfaces,we introduce the multidipoles expansion theory of electromagnetic scattering in detail.The specific derivation formula is listed,which is convenient for simulation calculation in the research.Finally,the simulation software used in our research is briefly introduced,mainly introduced CST and COMSOL which are common and frequently used simulation software.In Chapter 3,an ultra-high figure of merit(FOM)nanoscale refractive index sensor based on toroidal dielectric metasurfaces in near infrared region is proposed.The excitation of ultra-sharp TD resonance and local electromagnetic field enhancement between two semicircular silicon nanodisks are demonstrated.It is found that the geometric size of semi-circular silicon nanodisks is sensitive to the resonance half-height width(FWHM)and Q factor changes.The geometric parameters corresponding to the maximum FWHM and Q factors are obtained by optimizing the structural parameters.In addition,its sensor performance is also studied.The results show that FOM of our proposed toroidal dielectric metasurface sensor is much higher than that of published near-infrared refractive index sensors.Finally,also studied the analyte loss influence on resonant frequency,the results show that the refractive index is the main factor of the resonant frequency shift,and the loss of analyte.Therefore,dielectric metasurfaces sensors can be used as refractive index sensors for various materials.We expect that these findings will advance the development of metasurface sensors and that the proposed highperformance TD dielectric metasurface sensors will find applications in biochemical sensing.In Chapter 4,dynamic transmission control based on all-dielectric Toroidal dipole metasurfaces is proposed for grating.In this chapter,the application of all-dielectric toroidal metasurfaces to grating is described in detail.In this work,we study all-dielectric toroidal metasurfaces with dynamic transmission control in near infrared band.By analyzing indium tin oxide(ITO),a dynamic tunable material,the properties of ITO and the principle of tunable relative permittivity are described in detail.The designed alldielectric toroidal metasurfaces is combined with ITO to realize the dynamic control function of transmittance.An all-dielectric toroidal metasurfaces is designed to be applied to the grating according to the span in which the transmission is controlled.And the intensity of each diffraction level generated by the grating is calculated.In this section,we also introduce the content and research results of this work in detail from the structure design of metasurfaces,electromagnetic field analysis at resonant frequency,modes decomposition and the application of dynamic control of transmittance to grating.The last chapter summarizes and looks forward.