Graphene And Periodic Surface Composite Structures For Terahertz Absorption And Modulation

Two-dimensional graphene has attracted extensive attention in the fields of optics and electricity,for its unique electronic band structure provides excellent electromagnetic properties.In particular,its Fermi level can be dynamically changed by the external gate voltage,making graphene become an ideal material for optically tunable devices.In this research,based on graphene,combining the medium and metal periodic surface composite structure.We carried out detailed theoretical analysis and simulated research on the absorption and modulation of terahertz.The main research contents are as follows:We introduced surface plasmons,graphene electromagn etic properties and surface plasmons of periodic metal surface structures.It is verified by numerical calculation that the chemical potential changes can change the graphene conductivity and relative dielectric constant.We designed a broadband terahertz absorber based on continuous graphene and dielectric periodic surface structure,which consists of a silicon strip array,a continuous graphene layer,a polymer substrate layer and a metal substrate.First of all,we constructed a graphene-medium-metal composite absorption structure,studied its absorption characteristics,and discussed the influence of the chemical potential of graphene and the thickness of the polymer base layer on the absorption characteristics.Secondly,we explored the effect of the dielectric periodic array on the absorption properties of the above structures.The simulation results show that the interaction between the one-dimensional silicon strip array and the graphene-medium-metal composite structure can broaden the absorption bandwidth of the composite structure.The length and width of the silicon strip and the change in the length of the structural period all have an effect on the absorption properties of the composite structure.Finally,we designed a tunable broadband absorber based on continuous graphene and two-dimensional periodic silicon strip arrays.The simulation results show that the absorption bandwidth of the structure is 0.73-1.95 THz,that is,the frequency band with the absorption rate exceeding 90% reaches 1.22 THz.Analysis of the electric field energy distribution diagram at different frequency points shows that the resonance of the electromagnetic wave in the silicon strip array to the graphene surface plasma mode and the FP resonance formed by the continuous graphene layer produce a broadband absorption effect of the absorber.We discussed the effects of polymer thickness,graphene layer number,and graphene chemical potential on absorber performance.The structure size of the absorber was optimized to obtain the best structural design parameters.Compared with recent similar research results,the results show that the designed absorber bandwidth ratio is 91%,and it will be used in practical applications.Machining mean will.the absorber has excellent performance.We designed a terahertz modulator based on a graphene strip and a metal slit periodic surface structure.The structure consists of a metal slit array on the top of the silicon dioxide substrate and a graphene strip at the bottom.Firstly,we verified the transmission enhancement effect of the metal slit periodic array in the terahertz band,and discuss ed the effects of the polarization mode,incident angle and slit width of the incident wave on the transmission enhancement.Secondly,for the graphene strip array,it is verified that the chemical potential,strip width and period length of graphene affect the position of the resonance peak of the graphene strip array,and the electron relaxation time will affect the intensity of the resonance peak.Finally,we designed a terahertz modulator based on graphene array and metal slit array composite structure.Combined with the transmission spectrum and electric field distribution of the composite structure,it shows that the chemical potential of the graphene strip array determines its resonance peak and top metal narrow.The array of transmission peaks match the degree of switching,which in turn enables the modulator to be turned on and off.At the 1.03 THz,the modulator has a modulation depth of 98.99%.Fin ally,We analyzed all the effects of chemical potential,electron relaxation time and structure size on the performance of the modulator.