Study On Tunable Terahertz Metamaterial Based On Fano Resonance

Terahertz(THz)wave is usually defined as the electromagnetic wave between 0.1 THz and 10 THz.It has the properties of low photon energy,strong penetration,rich spectral information and wide communication bandwidth,so it has a broad application prospect in various fields,including substance detection,spectral analysis,telecommunication,and so on.As a new artificial design material,metamaterial(MM)can obtain controllable electromagnetic response by changing the geometric parameters or arrangement period of sub-wavelength structural units.In recent years,MM has been developed to provide an effective way to manipulate and modulate THz waves.Unlike the conventional plasmon resonance mode based on MMs,the resonance mode of Fano resonance based on MMs originates from the interference effect between the superradiant and subradiant plasmon resonance modes in the cell structure.Theoretically,Fano resonance can achieve much narrower spectral linewidth,stronger local electric/magnetic field enhancement effect and even higher refractive index sensitivity,which has important research significance in the frontier fields of biochemical sensors,optical switches and slow-light devices.Based on this,this thesis focuses on the structural design and characteristics of tunable THz MM based on Fano resonance.Two tunable THz MMs based on Fano resonance were proposed.The generation mechanism,tunability and application prospect of Fano resonance in two kinds of MMs were studied and analyzed.The main work are summarized and listed as follows:(1)A metal-graphene based THz MM is designed and investigated.It realizes the polarization insensitive Fano resonance by symmetrically nesting the gold splitresonant ring(SRR)and the monolayer graphene(MG)disk in the same structural unit.The tunability of the MM is investigated by numerical simulation of different structural geometric parameters,incident angles and graphene Fermi levels.The differences between the sensing properties of nanomaterials based on conventional plasmonic MMs and the Fano MMs are compared and analyzed.The results show that the Fano THz MMs is more suitable for nano-thickness sensing.The sensitivity is 1.18 THz/refractive index unit(RIU)for the 2-nm-thick analyte(1.00?n?1.56),and the maximum frequency shift of nanoscale thickness is 1671.61 GHz for the analyte(bromoform,n?1.56)in the thickness range of 2 nm to 40 nm.It provides theoretical guidance for the design of polarization-insensitive Fano-type THz MMs and the development of THz sensors for biological/chemical applications.(2)A MG ring-rod based plasmon induced transparent(PIT)THz MM is proposed,which forms a polarization sensitive transparent window in THz band through the interference phenomenon during mode coupling.The dipole-dipole interaction model and numerical simulation were used to study the influence of graphene structure spacing,graphene Fermi level and the polarization angle of incident light on PIT.The results show that the increase of the structure spacing will directly lead to the decrease of coupling strength;for the polarization angle of incident THz wave increases,the coupling strength decreases continuously.When the polarization angle reaches 60°,no obvious transparent window is observed,and when the polarization angle reaches 90°,the transparent window disappears completely.In addition,the influence of the polarization angle of incident THz wave on the slow light characteristics of the MM structure is investigated.The results show that the slow-light characteristics of the MM decrease with the increase of the polarization angle.The maximum group delay time corresponding to the polarization angle of 0 degrees is 136.57 fs,which shows obvious slow-light characteristics.This research has important application value in the development of slow light devices in terahertz band.(3)The gold SRR THz MM is fabricated by using the laboratory-made femtosecond laser micromachining system,and the electromagnetic properties of the THz MM are characterized by THz time-domain spectrometer.The experimental results are consistent with the simulation results.It is helpful for further development of THz functional devices and verification of numerical simulation.