| Electromagnetically induced transparency is a quantum interference effect that occurs in a three-level atomic system,which can make an opaque medium transparent and make the medium's absorption of probe light almost zero.The slow light effect and sudden increase in refractive index accompanying this effect make it of great application value in the fields of optical information storage and refractive index sensing.In traditional atomic systems,the realization of this effect usually requires harsh experimental environments such as ultra-low temperature and strong light pumping.The use of artificially synthesized electromagnetic materials such as metamaterials to simulate electromagnetically induced transparency not only overcomes this difficulty,but also The adjustable electromagnetically induced transparent window can be realized through light control,temperature control,electric control,etc.,which greatly expands the application prospect of electromagnetically induced transparency.In this paper,the electromagnetically induced transparent metamaterials are studied in the terahertz frequency band.According to the two coupling modes of metamaterials to achieve electromagnetically induced transparency effects,the metamaterial structures with metal and graphene as the main control materials were designed,and their electromagnetic response characteristics and performance were simulated and analyzed.The main research contents are as follows:1?An electromagnetically induced transparent metamaterial structure coupled by bright and dark modes is designed.Through the three-dimensional coupling of four open resonant rings and a planar closed square ring,the structure produced four electromagnetically induced transparent windows at 1.21 THz,1.46 THz,1.61 THz and1.98 THz,and the resonance intensity reached about 0.9.By splitting and comparing the cell structure and the surface electromagnetic field distribution,the coupling mechanism to realize the multi-band electromagnetically induced transparency effect is deeply studied.The influence of the size of the opening of the open resonant square ring and the size of the closed square ring on the strength and bandwidth of the EIT in the metamaterial is discussed.The application performance of the structure in slow light effect and refractive index sensing is analyzed.2?An electromagnetically induced transparent metamaterial structure with explicit mode coupling is designed.Through the strip graphene structure and the T-shaped graphene structure,the bright mode coupling effect is realized,and an electromagnetically induced transparent window is produced.The Fermi level of graphene is changed by applying a bias voltage,and the transparent window is adjusted.The effects of unit period,strip and T-shaped graphene structure width,and incident wave polarization angle on the response of electromagnetically induced transparent transmission in metamaterials are discussed.The Fermi level of graphene was adjusted,and the group delay,refractive index sensitivity,modulation depth and other performance indicators of the structure were studied.Simulation analysis shows that both of the above-mentioned metamaterials can achieve electromagnetically induced transparency in the terahertz band.The first three-dimensional metamaterial structure can achieve multi-frequency high-intensity slow light effects,and its group refractive index can reach 289.4,and it also has multi-band high refractive index sensitivity(658GHz/RIU);the second graphene metamaterial structure can Realize the adjustable slow light effect with a group delay of up to 173.13 ps and the dynamic adjustment of the refractive index sensitivity of 562.5GHz/RIU.Therefore,both structures have good application performance in the fields of optical buffer and refractive index sensing,and provide new ideas for the design of terahertz devices in the future. |
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