Study On Plasmon-induced Absorption Based On Metamaterials

Metamaterial（MMS）is an artificially synthesised periodic material with super-physical properties such as super-magnetism,negative refractive index and strong flexibility.In recent years,the maturity of vapor deposition and electron beam lithography has made it possible to prepare nanoscale metamaterials,which can purposefully and selectively control the absorption spectrum.In addition,nanoscale metamaterials based on BP and graphene have excellent optoelectronic properties,such as high carrier mobility,mechanical flexibility and dynamic tunability,which have promising applications in optical absorbers,optoelectronic sensors and electronic circuits.This paper focuses on the performance requirements of sensors,optical absorbers and other devices,and designs two multi-band perfect absorbers based on the nanoscale metamaterials of graphene and BP with selective tuning properties for absorption spectra,and explores their performance in the field of absorbers and sensors.The main research elements of the thesis are as follows:1、This chapter begins with an introduction to the history of 2D materials,their excellent optoelectronic properties and the preparation of several 2D materials.The discussion then focuses on two of the most widely known of the 2D materials:graphene and BP.Summarising the extensive previous work on graphene-BP,it is found that both graphene and BP support plasmonic excitations that can interact strongly with light to enhance the material’s absorption of light.The relatively special phenomenon of plasma-induced absorption in plasma excitations is also described.The use of this phenomenon can significantly alter the optical response spectrum of the material,increasing the absorption peaks of the absorption spectrum and enhancing the optoelectronic properties of the material.2、This chapter introduces the Finite difference method in the time domain（FDTD）,an important mathematical analysis method,and gives a history of the development of FDTD.The numerical stability of FDTD is then investigated,and the conditions for the stability of FDTD are obtained.And then the more special boundary condition in FDTD simulations,namely the perfectly matched layer,is introduced.Finally,the multi-dimensional coupled modes are carefully studied and the formulas are derived,focusing on the coupling between the four-dimensional coupled modes and deriving the energy conversion relations for the four-fold plasma-induced absorption.3、This chapter presents a tunable multi-narrowband perfect absorber which based on graphene and BP.By changing the structural parameters and adjusting the BP and graphene bands,different numbers of perfect narrowband absorption peaks can be obtained.Then,the physical energy transfer mechanism of the system was studied using CMT.The CMT calculation data are basically consistent with the FDTD simulation results,which proves that the optical equivalent cavity CMT can analyze the system well.The effects of structural parameters t₁,t₂ and L on the absorption spectra of the proposed structure were analyzed in detail,and the relationship between the system PIA and the vertical distance between the graphene and BP bands was studied.By changing the graphene Fermi level and BP carrier density,the dynamic tunable function of the structure can be realized.By adding a piece of BP₃ to the structure,the absorption peaks of the system changed from four to five.When the polarization angleθis less than 30°,the PIA phenomenon of the system is insensitive to the polarization angle.However,whenθequals 30°and 60°,the absorption efficiency is very different,proving that the PIA phenomenon of the system is very sensitive to the polarization angle at this time.Therefore,taking advantage of these excellent properties,the proposed structure may have potential applications in optical filters,switches,sensors,and absorbers.4、This chapter presents a graphene/BP based dynamically tunable and highly sensitive sensor.By adjusting the height of the grating,the strength of the structural PIA can be enhanced within a certain range.The effects of grating width and isolation layer height on the intensity of the optical response of the system are investigated.The energy transfer mechanism of the system is analysed using CMT theory,and the results show that the theoretical data of CMT fits well with the FDTD simulation results,which proves that the analysis of the proposed structure with an optically equivalent cavity is correct.Furthermore,by varying the Fermi energy level of graphene and the carrier density of BP,a dynamic adjustment of the absorption spectrum of the system can be achieved.Finally,the sensitivity and FOM（Figure of merit,FOM）of the system at the four detection points were analysed by varying the ambient refractive index.The maximum sensitivity and FOM are 5.174μm/RIU and 26.449,respectively.Thus,our proposed structure may provide a new way to design optical sensors and perfect absorbers in the mid-infrared band.