| Electromagnetically induced transparency(EIT)is an electromagnetic phenomenon that two electromagnetic waves with similar resonant absorption frequencies produce a sharp transmission window through electromagnetic coupling.The EIT effect has good engineering practical values because of its characteristics of slow light effect and high refractive index sensitivity.However,the realization and application of this effect are often limited by the harsh working environment such as ultra-low temperature and high light pumping.The metamaterial arrays manually fabricated by composite processing provide a new way to solve this problem.Through reasonable cell structure design and parameter configuration,artificial metamaterials can realize many special electromagnetic phenomena including this effect at selected frequencies under normal experimental conditions.Metamaterial's convenient use and flexible adjustability make it one of the most important research hotspots in the field of EIT.Based on the terahertz band,which is difficult for natural materials to respond directly,and aiming at multiband,broadband and tunable characteristic,which are relatively less studied by scholars at present,the suitable metamaterial structures and their applications are designed and analyzed.The main contents are as follows:1.A planar and vertical combination of metamaterial that can realize the multiband and broadband electromagnetically induced transparency effect by three dimensional coupling is designed.Through the coupling of three vertical split ring resonators(SRRs)and one planar square closed loop(SCL),the electromagnetic induced transparency of the metamaterial is realized at 0.68 THz and 1.09 THz.The bandwidth can reach 0.38 THz and 0.74 THz,respectively.By simulating equivalent circuit,comparing and splitting the structures,and discussing the edge effect of the structure,the physical mechanism of the multiband and broadband electromagnetic induced transparency are studied,besides,the influences of the distance between the three SRRs and their arm-lengths on the intensity and bandwidth of the electromagnetic induced transparency are analyzed.2.An active electromagnetically induced transparency metamaterial based on photosensitive gallium arsenide is designed.The photoelectric characteristics of gallium arsenide enable the peripheral circular closed loop(PCCL)of the metamaterial structure to respond to the electromagnetic waves of different frequencies under different illumination conditions,and it is coupled with the central split ring resonators(CSRRs),which can produce a strong electromagnetically induced transparency effect at the frequencies of 0.7 THz and 1.5 THz.By adjusting the intensity of light to change the conductivity of gallium arsenide,the equivalent circuit model of the proposed structure under various conditions is simulated.Combining with the comparison of split surface metal rings and the discussion of the edge effect,the photosensitivity of the metamaterial structure and the physical mechanism of the multiband electromagnetically induced transparency are analyzed.At the same time,the influences of the width of gallium arsenide,the opening size of SRRs and the thickness of substrate on electromagnetic induced transparency are studied.The results of simulation show that compared with the traditional single-band and narrow-band structure,the two metamaterials mentioned above can achieve high-intensity slow-light effects at multiple frequencies in terahertz band,with peak group refractive index of 211.6 and 184.7,respectively.Meanwhile,both of metamaterials have multiple wide refractive index sensing bands,in which their peak sensitivity can reach 0.51 and 0.46 THz/RIU,respectively.It can be seen that the two metamaterial structures have certain application value in the field of optical buffering and refractive index sensing. |
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