Design Of The Electromagnetically Induced Transparency Terahertz Metamaterial Based On Graphene

Electromagnetically induced transparency(EIT)refers to the quantum interference between different excitation pathways in atomic system,which leads to a transparent window for light within an opaque band.The accompanying properties including large group delay,high quality factor and frequency selective feature that exhibit potential applications in slow light,terahertz sensing and optical modulation.The analogy of EIT phenomenon based on planar metamaterials is an emerging research field that has attracted tremendous attention because it free scientists from cumbersome experimental environment such as laser pumping and low temperature.The metamaterial analogies of EIT also extend the range of its future application and can be dynamically manipulated by laser pumping,thermal tuning and electrical control.In this paper,the graphene-based EIT metamaterial is investigated according to the two basic coupling way i.e.the bright-bright coupling and the bright-dark coupling.Graphene metamaterials and meta-graphene hybrid metamaterials are designed and their transmission characteristics and performance are numerically calculated.Main contents are as follows:1.The mechanism of the EIT phenomenon in atomic system is illustrated.The mechanical harmonic oscillator and the circuit model are built to analyze the origin of EIT and the influence of the key parameters on transmission characteristics.The bright-dark couple in achieving EIT in metamaterials is investigated based on the study of the typical EIT structure.The slow light effect accompanied with EIT effect is elucidated.In addition,the conductive feature of the two-dimensional material graphene is analyzed.The variation of its surface conductivity with Fermi energy is discussed,which lays the foundation of the following research on tunable EIT metamaterial design.2.Typical EIT metamaterial based on bright-bright coupling is presented and the phase coupling process is analyzed.The metamaterial consisting of two resonators based on graphene rings with different radii is designed to generate the EIT phenomenon.By tuning the Fermi energy of graphene through electrostatically gating,the transmission of the metamaterial can be controlled dynamically and the amplitude modulation in two resonances can be achieved.Influences of the graphene ring and array period on the EIT effect are discussed.Performance indices such as modulation depth and sensing sensitivity are investigated.A metamaterial based on cut-wire metal resonators with graphene strip placed between them is designed.The destructive interference between two resonators gives rise to a transparency window.By tuning the Fermi energy through bias voltages,the transparency window can be manipulated dynamically.The efficient modulation is controlled only in the transparency window with slight changes in transmission dips,which may avoid the additional noises in adjacent frequency regions in the modulation process.3.An EIT metamaterial based on metal strips and horizontal graphene wires is presented.The EIT phenomenon can be induced by bright-dark mode coupling on condition of structural lateral displacement.Lorentz oscillation model is built to analyze the bright-dark coupling process.The effects of displacement and Fermi energy on the coupling coefficient,detuning frequency and damping rate are discussed.Moreover,another EIT metamaterial based on bright-dark coupling is presented which consists of U-shaped ring resonators as radiative element and cut-wire pair as dark element.The transmission curves can be electrically manipulated with different Fermi energy of graphene placed between the U-shaped ring and the substrate.By analyzing the surface distribution,the deformation of the transparency window is analyzed.The influence of the strip width and the carrier mobility is also considered.4.A symmetric structure composed of graphene pane and the inside metal cross-shaped strip is proposed which overcomes the requirement of the antisymmetric unit of the EIT metamaterial.The polarization-independent EIT effect is realized based on this structure.Meanwhile,a dual-window EIT metamaterial is constructed based on three horizontal metal strips with different length and the dual-region slow light effect is obtained.By placing the graphene strip between the adjacent metal strips,the influence of the graphene layer position and the Fermi energy on the transparency window as well as the slow light effect is analyzed.5.A mechanically and electrically controlled EIT metamaterial consisting of graphene patch array connected by horizontal wires is presented.By adjusting the incidence angle,the phase delay of the field distribution between adjacent graphene patches is induced and the destructive interference is generated,which leads to the transparency window.Dependence of the transmission characteristics on the illumination angle and the Fermi energy is investigated.Moreover,the varying trend of the transmission peak and the quality factor at extremely large incidence angles is explored.The variation of slow light performance with different incidence angles and Fermi energy is also discussed.This work provides strategies for realizing EIT effect in metamaterial,showing the advantages of graphene-based metamaterial in obtaining the tunable EIT phenomenon.The results of this study provide valuable guidance in designing and analyzing tunable EIT structures and offer new platform for designing graphene-based terahertz devices.