Terahertz Metamaterial Based On Functional Unit Enhanced Extraordinary Transmission

Terahertz waves(THz)are an important bridge between electronics and photonics in the electromagnetic spectrum.With its low photon energy,high carrier frequency and good penetration,THz waves have significant applications in fields such as biomedical,optical communications,and national defense.However,the THz band has always faced the problem of natural functional material resource scarcity.Exploring the physical problems of enhancing the interaction between THz waves and materials and realizing technological applications is key to further promoting the performance breakthrough of THz functional devices.In 1998,T W.Ebbesen et al.reported the phenomenon of extraordinary optical transmission(EOT)of small aperture arrays on metal films in Nature,achieving field enhancement and significant transmission intensity in the sub-wavelength scale,which quickly drew great interest from scientists around the world.After decades of research,it was found that the EOT effect in subwavelength metal structures is mainly due to the surface plasmon polaritons(SPP)excited on the metal surface by the external electromagnetic field.Current application development research based on this phenomenon has become a hot topic in the field of optics.Therefore,deeply understanding and revealing the essence of the EOT achieved by metal structures in the THz band lays a good research foundation for developing THz functional devices.This paper mainly uses the FDTD numerical simulation method to design,optimize,and study the performance of THz metamaterials that achieve enhanced EOT effects through a collective unit of metal hole arrays.Using graphene to achieve dynamic tuning of EOT,this paper proposes various modes of enhanced EOT THz functional devices.The main work of this paper is as follows:(1)A THz metamaterial functional device based on concentric hemispherical gold hole arrays that generate EOT is proposed.By introducing hemispherical particle functional units,the mutual coupling between surface plasmon polaritons around the hole and localized surface plasmon resonances(LSPR)excited by the gold hemisphere greatly enhances the locality of the electric field.Compared to traditional metal hole arrays,not only is the transmission intensity increased to 97%,but the half-peak full width is also widened by a factor of 9,and the structure size can be significantly reduced.By changing the shape and size of the central particle,the integrated structure’s enhanced EOT effect in the THz band is further verified.When gold particles are introduced into a traditional bull’s eye structure,the coupling between the periodic grooves generated SPP and the LSPR generated by the hemispherical particles also produces the EOT phenomenon.The maximum normalized area transmission peak of the bull’s eye structure with hemispherical holes can reach 556,significantly higher than that of the traditional bull’s eye structure.This novel design has guiding significance for future improvements in THz plasma devices.(2)A method for double-wavelength tunable EOT in a novel metal annular rod-nanobar structure using graphene has been proposed,where the double-enhanced transmission peaks are mainly generated from the excitation of LSPR.The integration of monolayer graphene into terahertz metamaterials causes changes in the plasmon distribution of the resonant surface,interfering with the generation of LSPR.Active tuning from double-to single-peak EOT was achieved by adjusting the Fermi level of graphene to a certain degree.When the graphene is placed under the rod,the peak transmittance of the device at the resonant frequency of 2.42 THz decreases to 6%as the Fermi energy changes from 0 to 0.5 eV;when the graphene is placed under the annulus,the transmission peak at the resonant frequency of 1.77 THz almost disappears as the Fermi energy changes from 0 to 0.7 eV.The remarkable tuning capability of the double-wavelength EOT indicates its broad application prospects in the areas of frequencyselective surfaces,communication,filtering,and radar.(3)A terahertz metamaterial device for enhanced extraordinary optical transmission(EEOT)based on Mie resonance coupling is proposed.By placing silicon particles on both sides of subwavelength metallic holes arranged periodically,the Mie resonance effect generated by the silicon particles localizes the incident light within the subwavelength scale of the particles,forming an extremely high-energy density equivalent electromagnetic dipole that is then radiated out through the small holes.When the radius of the hole is 17 times smaller than the resonant wavelength,the enhancement factor of the resonator-resonator coupling structure is 629 times that of the small hole structure alone.In addition,when analytes are placed at different positions on the silicon particle resonator,the terahertz metamaterial EOT device exhibits high sensitivity to the surrounding environment.The maximum sensing sensitivity can reach 51.56 GHz/RIU,and the sensor can detect analyte heights as low as 0.2 μm.This terahertz metamaterial device for transmission enhancement and sensing based on Mie resonance coupling of silicon particles has the advantages of high transmission efficiency,low loss,and strong compatibility with current semiconductor processes.