Multi-mode Electromagnetic Induction Transparent Control Based On Terahertz Metamaterials

Electromagnetically induced transparency(EIT)is a quantum interference process that was found in a three-level atomic system,which is caused by the quantum destructive interference between different transition pathways.It forms a narrow transparency window in a broad absorption spectrum,so that light can propagate freely through an initially optically opaque medium,meanwhile,it is accompanied by strong dispersion and large group velocity,leading to slow light and nonlinear effects.However,the realization of EIT effect in quantum field needs harsh conditions,such as high intensity lasers and cryogenic temperature environment,which greatly limits the development of EIT.As the development of metamaterials,EIT effect can be realized by the destructive interference between a bright mode and a dark mode or a quasi-dark mode in metamaterial,operating at the room temperature.Therefore,metamaterial EIT has attracted extensive attention of researchers.In this paper,we study the EIT effect of structural modulation and polarization modulation in theory and simulation.The main research contents and conclusions can be summarized as follows:1,Three kinds of resonators based on terahertz metamaterials are designed,split-ring resonator(SRR),T-type resonator(TTR)and coupled split-ring resonators(CSRRs).The transmission spectra of these three resonators are fitted by Fano fitting,coinciding excellently with the FDTD simulation.Combined with its electric field intensity distribution and Q factor,it is shown that: When the incident light is x-polarized,the TTR acts as the bright mode,the CSRRs act as the quasi-dark mode and the SRR acts as the dark mode.When the incident light is y-polarized,the TTR acts as the bright mode,the CSRRs act as the dark mode and the SRR acts as the quasi-dark mode.In addition,the proposed structure is simulated and analyzed by means of structural modulation.By increasing the spacing of resonators,we can clearly find that the EIT transmission peak intensity is weakened in varying degrees,which is caused by the weakening of coupling between resonators;By increasing the unit structure period,the EIT transmission peak intensity is significantly enhanced;By increasing the refractive index of the substrate,we can see that the EIT transmission window has a significant red shift.2,A terahertz metamaterial with EIT mode actively controlled by polarization of incident light is proposed.When the incident light is x-polarized,there is a coupling between the T-type resonator as a bright mode and the coupled split-ring resonators as a quasi-dark mode.An EIT transmission window is formed due to the destructive interference.Combining the three-level EIT system and the electric field intensity distribution,the generation mechanism of a single EIT transmission peak is analyzed in depth.Under the y-polarized incident light,the terahertz metamaterial can produce dual EIT modes,which come from the destructive interference of the TTR(as a bright mode),the SRR(as a quasi-dark mode)and the CSRRs(as a dark mode).Combined with the four level EIT system and the electric field intensity distribution,the generation mechanism of the two EIT transmission peaks is analyzed.Changing the incident light from x-polarization to y-polarization,we can achieve a transition from single EIT mode to dual EIT modes.Lorentz coupling model is used to analyze the mechanism of EIT mode under different polarization.At the same time,the slow light effect can also be controlled by polarization.Under x-polarized illumination,one slow light wave packet is observed,related to a group delay of 9.93 ps.Under y-polarization,dual slow light effects and a larger delayed wave packets are observed,and the group delays reaching 9.31 ps and 11.10 ps respectively.