Research On Structural Design And Performance Of Graphene-based Multi-functional Metamaterials In Infrared Band

Infrared radiation refers to electromagnetic waves with wavelengths between the terahertz and visible bands,which usually include three important atmospheric windows,consisting of near-infrared,mid-infrared and far-infrared,respectively.Compared with devices operating in other wavelength bands,infrared optical devices have a wide range of promising applications in military,biomedical,environmental,and aerospace.Conventional infrared optical systems require the combination of multiple devices and the structures in the system are discrete and functionally specific.These devices have many problems such as complex structure,small flexibility,and large size.The emergence of metamaterials has fundamentally opened up new mechanisms for the interaction of light with matter.For different needs,researchers can choose different types of metamaterial structures for various purposes of manipulating light.There is no doubt that metamaterials allow infrared optical devices to show great potential for applications.Driven by the above application background,this thesis investigates the properties of graphene-based metamaterials in the infrared band to provide theoretical guidance for the development of multifunctional,miniaturized,chip-based and integrated infrared devices.The main research includes the following sections:A graphene-based hyperbolic metamaterial structure is designed to achieve beam manipulation in the mid-infrared band.Graphene-based hyperbolic metamaterials are multilayer structures formed by periodic stacks of graphene and dielectrics.By tuning the graphene Fermi level in the structure,the in-plane and out-of-plane equivalent permittivity of the multilayer structure are made positive and negative,and the tuning of the Fermi level to the iso-frequency curve type is achieved.By selecting a specific wavelength and Fermi level,the iso-frequency curve switches between elliptical and hyperbolic.Based on this principle,two large-angle,wide-band tunable optical switches with positive and negative refraction are realized.Finally,a hyperprism structure for beam manipulation is designed and implemented.By tilting the main axis of the graphene-based multilayer metamaterial,a special hyperbolic isofrequency curve tilted at the hyperprism-air refractive layer interface is obtained,resulting in a total reflection,highly transmissive optical switch function.In addition,in the on state,the angle of beam steering depends on the variation of the incident angle and the tilt angle of the main axis of the hyperprism.Beam steering is achieved by varying the incident angle and the Fermi level.This structure allows both optical switching and beam steering to be adjustable at large angles.The anti-ring metamaterial structure with C₂symmetry was designed to achieve the angle-tuned surface lattice induced transparency effect in the infrared wavelength（7.5-15μm）.The anti-ring metamaterial array structure consists of a periodic metal-symmetric anti-ring,a graphene layer,and a dielectric substrate.Firstly,the incident pitch and azimuth angles are adjusted to induce surface lattice resonance modes in the infrared band.Secondly,the trapped mode is generated in the symmetric structure by tuning the incidence angle.The dependence of the coupling between the modes on the polarization state and the incident angle is investigated.The single-mode modulation in TE polarization and multi-mode coupling in TM polarization are realized respectively.Finally,using the mode characteristics of surface lattice resonance at different incidence angles and polarization states,the gas sensing function is realized in the TE polarization state.And the single and double induced transparency effects are realized in the TM polarization state.By dynamically adjusting the pitch angle,the transparent window is able to achieve modulated switching effects.Changing the Fermi level can change the position of the transparent window and the transmission intensity of the transparent peak to achieve an adjustable delay bandwidth product.A space-filling fractal metamaterial structure is designed to achieve broadband absorption in the far infrared band.First,the coupling of localized surface plasmon resonance of metamaterials and propagating surface plasmon resonance of resonant cavities,is used as the basis for broadband absorption.Second,the effect of the order of the space-filling fractal on the size and number of gaps is analyzed to investigate the modulation of absorption enhancement and widening bandwidth by gap plasmon resonance.Two space-filling fractals are used to achieve broadband absorption in the far infrared,respectively.The first one is a graphene-based first-order Hilbert fractal metamaterial structure that achieves broadband absorption at 19.5-40.5μm.The adjustable Fermi level of graphene can be efficient absorption switching regulation for broadband absorbers.The second is a Cr-based second-order Peano fractal metamaterial structure that achieves broadband absorption in the atmospheric window region or 12.3-32μm.Finally,the second-order quasi-Peano fractal designed to obtain polarization-insensitive broadband absorption by analyzing the effect of gap and gap plasmon resonance on absorption and balancing the number of gaps in the x and y directions.The absorption enhancement of these metal（graphene）-dielectric-metal based triple-layer device are attributed to the coupling effect between localized surface plasmon resonance,propagating surface plasmon resonance,and gap plasmon resonance.