Research On The Optical Absorption Characteristics Based On Graphene-grating Composite Structure

Graphene is a honeycomb-shaped two-dimensional material consisting of a single-atomic-thick carbon atom.Unlike metals,free carrier density of graphene can be controlled by chemical doping,gate voltage,electric field,magnetic field.As a result,graphene provides electrical tunability that is not available in conventional metal materials.In addition,its unique electronic structure impacts itself many excellent properties,such as high Fermi velocity,high carrier mobility,high transmittance,high thermal conductivity and low resistivity and so on,which sparked tremendous research interests ranging from material,physics and chemistry to biology.Based on this,we proposed three different graphene devices.The absorption properties of these kinds of structures were systematically studied by finite-difference time-domain method(FDTD)and rigorous coupled wave analysis(RCWA).The main contents of this thesis are listed below:(1)We have studied the material properties of graphene,including the conductivity and dielectric constant of graphene.On the basis of this,the interaction between electromagnetic wave and graphene is also studied.(2)We have designed a graphene/multilayer subwavelength grating structure.Without plasmonic response,the single-channel perfect absorption is associated with critical coupling,which is enabled by the synergetic effect of the guided resonance and photonic band gap(PBG)of the system.Simulation results demonstrate that critical coupling can be tuned by varying the structural parameters or simply modulating the incident angle.The absorption peak can be modulated by gate voltage on graphene monolayer.Especially,the enhanced resonant modes can be longitudinally coupled deep into the system and effectively enhance light-matter interaction.This total absorption offered by our design can hold potential in engineering many optoelectronic devices.(3)We have designed a graphene/dielectric grating/metallic film/dielectric multilayer structure.Based on critical coupling of guided resonance in combination with Tamm plasmon polaritons(TPPs)resonance modes,we achieve a dynamically tunable dual-channel perfect light absorption.We demonstrate that the high absorption peaks can be modulated by altering the geometrical parameters or dynamically controlling the chemical potential in graphene layer.More significantly,due to the multiple resonance modes in different wavelength channels,electric field in different layers of device can be selectively enhanced to realize nearly perfect absorption in either graphene sheet or dielectric multilayer.This work offers a new paradigm for selectively enhancing light-matter interaction through coupling of multiple resonance modes,and the proposed device will provide potential applications in multiple-channel photonic detection,sensing,communication and nonlinear nano-optics.(4)We have designed a deep metallic grating/dielectric/graphene monolayer multilayered structure.Strong coupling between the cavity resonance modes in periodic metal slit arrays and the graphene plasmonic modes gives rise to a pronounced spectral splitting and delivers a 100% perfect absorption.Calculation results show mode coupling and absorption response in this structure are closely associated with the geometric parameters and the optical property of graphene.Especially,it is indicated that mode coupling strength can be modified via dynamically adjusting the chemical potential of graphene layer,significantly delivering a flat-top perfect absorption spectrum as well as a selectively enhanced electric field in this proposed system.The intense absorption performance and the selective electric field enhancement offered by this plasmonic coupling regime will provide potential applications in light detection,sensing and nonlinear nanophotonics.