Design Of Dynamic Modulator And Absorber Based On Graphene In Terahertz

Terahertz wave is a kind of electromagnetic wave located in a special part of the electromagnetic spectrum.Because of its peculiar properties,terahertz wave has attracted the attention of researchers.It is also highly expected in different fields such as communications,national defense,and imaging.Graphene is a single-layer material shaped like a honeycomb,its thickness is negligible,and it has many advantages,such as lightness,thinness,and dynamic tunable.Based on these characteristics,graphene is often used as a modulation material for various terahertz devices to achieve its dynamically tunable function.Various graphene-based dynamically tunable devices have been reported,including absorbers,filters,and modulators.In this paper,we design two terahertz modulators and one absorber by applying graphene materials to terahertz metamaterials,which is the following:1.A modulator based on the plasma-induced transparent(PIT)effect is proposed.The metamaterial induces electromagnetically induced transparency through the strong near-field coupling between the metal cross-shaped structure and the split ring structure.The metamaterial can realize the function of adjusting the amplitude of the incident terahertz wave by changing the above bias voltage.The advantage is that there is no need to change the structure and size,as long as the bias voltage of the graphene is changed,the active control function can be realized more conveniently and effectively,and the modulation depth can reach 85%.Since the above modulator can only be used in one electric field polarization mode,a PIT effect modulator using pure graphene as the structure is then proposed,which can realize PIT effect in two electric field polarization modes of x and y respectively.Through theoretical analysis,the PIT effect of bright mode and dark mode coupling can be realized in the terahertz waves polarized along x diraction;but the bright mode and the bright mode are coupled with each other in the terahertz waves polarized along y diraction.By changing the refractive index of different environments,the sensitivities under the x and y polarization modes can be calculated to be 819.77 GHz/RIU and 538.37 GHz/RIU,respectively.In addition,adjusting the graphene Fermi level(0.5-0.8 eV)can achieve modulation of the PIT metamaterial transmission spectrum and slow light effect,and the group delay of the two polarization modes can reach 0.948 ps and 0.78 ps,respectively.Therefore,the PIT metamaterials proposed in this paper can promote the development of biosensing and slow-light devices.2.A three-frequency perfect absorber is designed using a pure graphene structure,which can realize dynamic adjustable characteristics.The structure of the absorber is composed of four graphene strips and graphene cross bars.It can be seen from the simulation results that the absorber has three perfect absorption bands at 0.93 THz,1.54 THz,and 2.4 THz,and the absorption efficiency is 99%,98%,and 99%,respectively.Through electric field analysis,it is found that the three perfect absorption bands should originate from the resonance of the graphene cross bars and the four bar graphenes.By changing the chemical potential of graphene,the frequency and absorption efficiency of all three frequency bands can be actively adjusted.In addition,we found that these perfect absorption bands are not sensitive to the incident angle and incident polarization angle,which makes the proposed absorber attractive in practical applications.We hope that this work will promote the engineering design of the perfect multi-band terahertz absorber and its application in detectors and sensors.