A Dynamically Tunable And Wide-Angle Terahertz Absorber Based On Graphene-Dielectric Grating

Terahertz waves refer to electromagnetic waves in the frequency band of 0.1 THz to 10 THz,which are in the transitional area from macro-classical theory to micro-quantum theory and from electronics to photonics.Terahertz waves have excellent physical properties and have been widely used in medical,security and other fields.They also show great prospects in the field of mobile communication technology in the future.The terahertz absorber based on the grating structure uses the interaction of electromagnetic waves and substances to convert radiant energy into other forms of energy,which is the basic device in the terahertz technology.Currently,super surface terahertz absorbers often work at a single frequency,which is inconsistent with the development trend of miniaturization and integration of terahertz devices.Graphene has strong interaction with electromagnetic waves due to its unique energy level structure,and this interaction has dynamic adjustable characteristics,which is widely used in the design of terahertz devices.Herein,a tunable terahertz absorber based on graphene grating is designed and studied.The details are as follows:A tunable terahertz absorber based on double-layer graphene grating structure was theoretically analyzed and simulation designed,which is consisted of double-layer graphene,dielectric grating and bottom metal substrate.The results show that when the chemical potential of graphene increases from 10 me V to 150 me V,the absorption frequency of the absorber moves from 1.015 THz to 1.165 THz,and the absorption efficiency can reach 99%.Through the study of the near-field distribution of the electromagnetic component of the device at the absorption frequency,it is found that the efficient absorption originates from the magnetic resonance between the double-layer graphene.The adjustable range of the absorption frequency is further controlled by designing geometric parameters.In addition,magnetic resonance has good symmetry,and the absorber can maintain good absorption performance at a wide incident angle of 0° to 60° under transverse magnetic(TM)polarization.A terahertz absorber based on a three-layer graphene grating structure is designed.The increase in the number of graphene layers improves the interaction between the structure and the incident electromagnetic field,and the absorption efficiency is further improved.After optimization and adjustment of the structural parameters,the working frequency of the absorber is 3.7 THz under the incidence of both TM polarized light and TE polarized light,achieving the polarization-independent function.A terahertz absorber composed of double-period graphene grating is studied.Adjacent graphene-silicon layer structures which have different widths are assembled into a supercell form.These two grating structures with different widths interact strongly with the incident light at frequencies of 1.015 THz and 0.095 THz,respectively,forming two absorption peaks.And because of the overlap between these two frequency bands,the increasement of bandwidth are achieved.The graphene grating terahertz absorber designed in this paper has the characteristics of tunable operating frequency,polarization-independent,and large bandwidth.It enriches the functions of terahertz absorber and promotes the development of terahertz technology.