The Study Of Terahertz Plasmon-induced Transparency Effect Based On Graphene Metamaterials

Metamaterials have aroused extensive attention owing to their significant scientific research values and revolutionary application prospects in many cutting-edge areas.Special electromagnetic properties not found in nature can be realized in metamaterials by means of rational structure design,which can be utilized to well overcome the bottleneck of material and functional device shortage in the terahertz regime.In addition,graphene,as an emerging two-dimensional material,has excellent and tunable electrical and optical properties.It is currently considered to be the most potential surface plasmon material in the terahertz to the far-infrared regime and possesses unique superiority in constructing tunable terahertz metamaterials.In recent years,the plasmon-induced transparency(PIT)effect is a research hotspot in the field of metamaterials.The metamaterial-based PIT device can not only avoid the harsh operating conditions required to excite the quantum phenomenon of electromagnetic induced transparency(EIT)but also overcome the limitations of the material and the working frequency range.Therefore,in this dissertation,based on the theoretical and experimental researches of metamaterials,by combining metamaterials with graphene or other adjustable semiconductor materials,a variety of tunable plasmon-induced transparency devices in the terahertz to the far-infrared regime are proposed and studied.The main research contents and innovative points are summarized as follows:1.The numerical calculation methods,experimental preparation and testing technologies of terahertz metamaterials are investigated.We put forward a design of double reverse nested split-ring resonator(SRR)metamaterial.An improved effective parameter retrieval method is used to investigate its effective parameters under normal incidence.Moreover,a modified H-shaped metamaterial structure are also proposed.Taking this structure as an example,the chemical exfoliation fabrication method and the measurement method of terahertz metamaterials are discussed in detail.The experimentally measured results of the fabricated metamaterial sample agree well with its theoretical simulation results,which validates not only the feasibility of the fabrication method but also the credibility of the simulation method.2.Two novel designs of tunable terahertz PIT metamaterials based on periodically patterned graphene structures are investigated.They exhibit prominent transparency windows,which are respectively attributed to the destructive interferences between the dipole plasmon resonance and the inductive–capacitive(LC)resonance or the monopole plasmon resonance.Tuning the Fermi energy in graphene results in the modulation of the transparency windows,allowing for the active control of the group index.3.A grating-coupled double-layer graphene hybrid system is proposed,which shows tunable PIT properties in the far-infrared regime.Based on the guided mode resonance principle,a diffractive grating is used to couple the normally incident waves and excite the plasmonic resonances on two graphene films separated by a spacer,thereby avoiding the need for patterning graphene.It is found that the origin of the observed transparency window transforms from Autler-Townes splitting(ATS)to EIT as the separation distance between the two graphene films increases.4.The biosensing characteristics of a terahertz PIT metamaterial based on hybrid graphene-gold structure is investigated.It exhibits a sharp PIT peak and excellent polarization-independent property.The PIT peak possesses a highly sensitive response to the change in the surrounding medium's refractive index.A sensitivity of 3.04 THz/RIU for the PIT-metamaterial-based sensor is obtained.In addition,the PIT peak can be tuned by controlling the Fermi level in graphene.Therefore,for different analytes,we can dynamically adjust the operating frequency of the PIT peak to ensure that the analyte can fully interact with the terahertz waves.5.An optically-controlled reconfigurable hybrid metamaterial waveguide system at terahertz frequencies is proposed to obtain high quality(Q-)factor induced transparency peak.By adding a waveguide layer in the substrate of the gold cut wire array,we obtain two narrow PIT peaks in the broadband dipole plasmonic transmission spectrum.Moreover,photosensitive semiconductor gallium arsenide pads are inserted between the gold cut wires.As the pump illumination increases,the system realizes the conversion from a double PIT material to an ultra-narrow band guided mode resonance filter with Q-factor up to 578.