| Electromagnetically induced transparency(EIT)is an atomic physical phenomenon,which is characterized by the decrease of the absorptivity of the material to the incident wave,showing “transparency”.Traditional implementation conditions require ultra-low temperature and strong light pumping,which severely limits its application,while metamaterials can avoid stringent conditions to achieve EIT-like.At present,most of the EIT-like metamaterials in terahertz band are passively controlled and can’t meet the requirements of practical applications.The study of active tunable EIT-like metamaterials in terahertz band is of great significance in the fields of optical buffer,sensor,modulator and so on.In this dissertation,the metamaterial structures based on graphene and gallium arsenide are studied,and the related characteristics of active tunable EIT-like metamaterials in terahertz band are discussed.The main work is as follows:1.An active tunable EIT-like metamaterial structure based on graphene is studied,which is insensitive to the polarization direction and incident angle of incident wave.Firstly,the metamaterial structure is constructed by using graphene strip and two Lshaped graphene resonant units,and the weak coupling between two bright modes leads to EIT-like effect.Then the pattern is rotated and mirrored to obtain a metamaterial structure composed of a cross-shaped structure and a 4L-shaped structure.The physical mechanism of the metamaterial structure producing EIT-like effect is investigated,and the effects of geometric parameters of metamaterial structure,polarization direction and incident angle of incident wave on the transparent window are analyzed,which can be effectively applied to the fabrication of omni-directional devices.The active tunability of the metamaterial structure is studied,and the active regulation of the transparent window can be realized by controlling the Fermi energy level of graphene materials.It is calculated that within the specified adjustment range of the Fermi energy level of graphene,the refractive index sensitivity of the metamaterial structure can reach 411GHz/RIU,and the maximum group delay can reach 0.81 ps,which can play an important role in high sensitivity refractive index sensing and has application potential in the field of optical buffering.2.A dual-band optionally regulated EIT-like metamaterial structure based on graphene material is designed.Two graphene split rings and graphene strip are coupled in dark-bright-dark mode,forming transparent windows near 1.19 THz and 1.57 THz,respectively.By splitting the structure and combining with the three-particle coupling model,reason for realizing the dual-band transparent window of the metamaterial structure is analyzed,and the effects of the opening size of the split ring and the distance between the split ring structure and the graphene strip on the transparent windows are studied.The transparent window and group delay window can be selected and regulated by adjusting Fermi energy level of graphene materials.The optional regulation performance is excellent,and it has the potential of fabricating terahertz wave modulator.3.A metamaterial structure composed of metal material and gallium arsenide is designed.By adjusting the external infrared light intensity,the coupling mode changes from bright-dark mode to bright-bright mode,which produces obvious EIT-like effect near 0.91 THz and 1.59 THz,respectively.Combined with the electric field and current distribution,the physical mechanism of the formation of transparent windows in the two bands are analyzed,and the effects of the width of gallium arsenide and the distance between the two structures on the two transparent windows are explored.The maximum group delay of the two transparent windows is calculated to be 4.64 ps and 2.18 ps,respectively,and the refractive index sensitivity is 103 GHz/RIU and 133 GHz/RIU respectively,which has great application value in optical information processing and has the ability of refractive index sensing. |
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