The Terahertz Slow Light Effect Based On Spoof-LSP Induced Transparency

In recent years,Metamaterial,as a kind of artificial composite material,has attracted wide attention from large numbers of researchers due to the exotic properties beyond the natural occurring materials.Spoof localized surface plasmon(Spoof-LSP)is a bound electromagnetic mode that exists in periodically textured metal structures with properties resembling those of the LSP in the optical regime.Spoof-LSP is an extension of LSP in low frequencies,which opens up a new path for designing compact,ultra-thin,microwave and terahertz plasman functional devices.According to these research focuses,we investigate the terahertz slow light effect based on Spoof localized surface plasmon-induced transparent window in this paper.By combining experiment with theory,we study the electromagnetic response characteristics of the metarmaterial and the physical mechanism of the metamaterial to achieve controllable terahertz slow light,including the feasibility of terahertz slow light devices with high group delay.The main work of this paper is as follows:1.We experimentally demonstrated a flexible planar metamaterial with a maximum group delay of more than 42.4 ps.The metasurface consists of an annular textured closed cavity and metallic arc.By adjusting the central Angle of the metallic arc,the intrinsic dipole mode of the metallic arc is in destructive interference with the spoof localized surface plasmon(Spoof-LSP)on the textured closed cavity,resulting in plasmon-induced transparency.The terahertz time-domain spectroscopy was used to measure the transmissibility of the prepared samples,and the numerical results of the extended coupled Lorentz oscillator model were verified.The results show that the coupling coefficient and damping ratio of the structure depend on the radius of the annular closed cavity ring structure.Therefore,at a specific frequency of the induced transparent window,the maximum of slow light becomes adjustable in intensity2.We demonstrate a polarization insensitive terahertz slow light in spoof localized surface plasmon induced transparent window.Two types of metasurfaces based on different lattice layouts,namely C₂ and C₄ lattice symmetry,are compared.The metasurface with C₂ lattice symmetry shows a slow light effect of 5 ps in the transparent window at 0.3 THz,while the metasurface with C₄ lattice layout can achieve a maximum group delay of 28 ps at 0.3 THz.The coupling coefficient and damping ratio of the transparent window of the metasurface based on the symmetric lattice layout of C₄are 5 times that of the metasurface based on the symmetric lattice layout of C₂.In the metasurface with C₄lattice symmetry,the constructive interference of the two eigenmodes introduces a positive group delay in the transparent window,while in the metasurface with C₂lattice symmetry,the superposition of the two eigenmodes forms a transparent window without obvious coupling.The results show that the point group symmetry or lattice structure of the metasurface has a great influence on the group velocity of the terahertz pulse,which provides flexibility for the design of polarized insensitive slow light devices in terahertz communication.3.We propose a polarization insensitive terahertz array induced transparent metasurface with embedded square lattice.The lattice consists of two sublattices with the same period,one is an annular closed cavity with periodic grooves,and the other is a metallic cross.The polarization insensitively plasmon induced transparency phenomenon appears in the terahertz transmission spectrum,and the maximum group delay is predicted to be up to 30 ps at the transparent window of 0.37 THz.The simulation results of the metasurface transmittance verify the numerical simulation results of the coupled Lorentz oscillator model.The collective eigenmodes of the two lattices are coupled by diffraction to form destructive interference in the same phase,resulting in an induced transparent window,where the group delay achieves the maximum and the electrical susceptibility is close to zero.