Study On Group Slowing Characteristics Of Terahertz Waves With Cavity-integrated Metallic Grating

Designing terahertz wave group velocity control devices is crucial for the terahertz communications on base of a new mechanism.The mechanism is proposed to generate the electromagnetically induced transparency analogue through the degeneracy of cavity-mode resonance and guided-mode resonance in subwavelength cavity-integrated metallic grating,and the control characteristics of terahertz wave group velocity by tuning the graphene Fermi level is studied in this thesis.The terahertz spectral response of the subwavelength metallic grating and cavityintegrated metallic grating are investigated in the paper.It is confirmed that a new mechanism is proposed to produce electromagnetically induced transparency analogue phenomenon from subwavelength cavity-integrated metallic grating when the guided-mode resonance and cavitymode resonance are simultaneously excited at a degenerate state.Using the coupled mode theory model,the physical mechanism of electromagnetically induced transparency produced by subwavelength cavity-integrated metallic grating is deeply analyzed.The group velocity slowing characteristics of terahertz wave in subwavelength cavityintegrated metallic grating are studied.Based on the electromagnetically induced transparency analogue phenomenon generated by subwavelength cavity-integrated metallic grating,the terahertz wave group delay is calculated to reach 3.44 ps.After further optimizing the structural parameters,the refractive index of the cavity filler is changed,and the change of the group velocity slowing characteristics of terahertz wave of subwavelength cavity-integrated metallic grating is analyzed.It is determined that the higher the refractive index of the filler,the greater the group delay.When the refractive index of the filler reaches 2,the group delay is as high as5.69 ps.These works lay a research foundation for the subsequent regulation of terahertz wave group velocity moderation by graphene.The change of group velocity delay of terahertz wave regulated by graphene is studied.The change of terahertz wave spectral mode after graphene is laid on the subwavelength cavityintegrated metallic grating is discussed.The phenomenon of electromagnetically induced transparency and the change of group velocity delay of terahertz wave are studied.It is determined that graphene significantly affects the slowing characteristics of terahertz wave group velocity.The influence of different refractive index cavity fillers on the electromagnetically induced transparency analogue phenomenon and the slowing characteristics of terahertz wave which are produced by the graphene controlling subwavelength cavity-integrated metallic grating are discussed.When the refractive index of the filling in the cavity is 2,the graphene has the greatest influence on the group velocity delay of the terahertz wave.Besides,the effect of changing the Fermi level of graphene on the electromagnetically induced transparency analogue phenomenon and the terahertz wave group velocity delay characteristic of the subwavelength cavity-integrated metallic grating is analysed.When the Fermi level of graphene increases by 0.3 e V,the frequency position at the electromagnetically induced transparency peak does not change,and the group delay increases by 7.97 ps,up to 23.23 ps.The terahertz wave group velocity is dynamically tunable without changing the geometric parameters of the structure.In the paper,the new mechanism presents a dynamically tunable electromagnetically induced transparency analogue of a subwavelength cavity-integrated metallic grating by the coupling of the guided-mode resonance with cavity-mode resonance in the terahertz regime.The group delay exceeds 23 ps when introduces the graphene overlying on the grating.The slowing characteristics of the terahertz wave group velocity can be controlled by tuning the graphene Fermi level which has excellent performance with stable working frequency and large tunable range.The research results provide an efficient scheme to manipulate the group velocity of terahertz waves.