Research On High-speed Modulation Mechanism And Devices Of THz Wave Based On Metamaterials

With the rapid development of Terahertz Science and technology,terahertz wireless communication has become an important branch of terahertz science.How to modulate terahertz signal efficiently has become an important problem in terahertz wireless communication.In this dissertation,the latest development of terahertz high-speed modulation devices is analyzed and investigated;the double-layer transmission type terahertz polarization converter based on ametamaterials is designed and studied,and the transmission type terahertz polarization converter with good polarization conversion effect is realized;the high-Q element surface based on ametamaterials structure is studied,and the high-Q element surface design based on tip coupling effect is realized;the experimental processing is completed HEMT single tube with good working effect.After completion of the above theoretical and experimental preparations,the artificial microstructural elements loaded with HEMT are placed in the waveguide transmission line,and the reconfiguration of the artificial microstructural elements is realized by controlling the HEMT's interruption,thus the electromagnetic waves transmitted in the waveguide transmission line are modulated.After investigation,simulation and experimental processing,high-speed waveguide-loaded terahertz modulator with high-speed modulation effect has been preliminarily completed.Based on this modulator,a part-modulated terahertz wireless communication system is built,and various performances of the device are tested experimentally,which verifies the feasibility of the system.The main research contents of this dissertation are as follows.1.A double layer terahertz polarization converter based on materials is proposed.Through theoretical analysis and simulation,the electromagnetic response characteristics of material structure and the influence of cell structure on the bandwidth and polarization conversion efficiency of the polarization converter are studied.Experiments show that in the range of 0.25-0.65 THz,the polarization conversion rate is more than 75%,and at 0.43 THz,the conversion rate is up to 90%.For the problem of polarization converter to the polarization direction of incident wave,an arbitrary incident linear thz wave polarization converter is proposed.The simulation and experiment results show that the polarization converter have a good polarization conversion for arbitrary incident terahertz wave near 0.9 THz.2.According to the resonance mode in the artificial microstructure,the different methods of producing high Q value are analyzed and compared.It is proposed to rotate the metal triangle in the metamaterial to obtain high Q value.Through simulation and theoretical analysis,it is found that when the rotation angle is close to 75 °,strong coupling can be obtained,which greatly improves the Q value,and the correctness of the above theory is verified by experiments.The influence of tip distance and charge accumulation on the tip electric field and Q value is analyzed by simulation,and the influence of tip charge accumulation density on Q value is verified.3.Through analysis and comparison,microstrip line and coplanar waveguide are selected as the transmission line of loaded modulation unit,whose central transmission line can not only guide terahertz wave to transmit energy,but also load modulation signal into HEMT transistor,so as to reduce the complexity of structure design and reduce the difficulty in design and processing.A 220 GHz waveguide microstrip transmission line is designed according to the actual demand.The influence of different structures on electromagnetic transmission is studied by theory and simulation.On this basis,the modulation unit structure which can be loaded with HEMT structure is modified and designed,and its feasibility is proved by simulation.After the modulation unit is loaded on the microstrip transmission line,the whole structure is simulated and demonstrated.The simulation model is transformed into the actual machining model,and the cavity assembly for the test is completed.On the basis of 220 GHz microstrip modulator,a 310 GHz coplanar waveguide high-speed modulator is designed and simulated,and the fabrication and assembly are completed.4.Static and dynamic tests are carried out on the processed THz high speed waveguide modulator.Static test is mainly to test the static performance of the device.The dynamic test can analyze the modulation depth,modulation rate of the waveguide loaded high-speed terahertz modulator.Finally,it is confirmed that the 220 GHz microstrip modulator has the highest modulation rate of 38 GHz for single frequency point signal.Then,the test and analysis of each part of the terahertz communication system are carried out.It is proved that the communication system can realize the baseband signal transmission of 1.7-3.7GHz,which can meet most of the experimental and test transmission needs.In the static test of 310 GHz coplanar waveguide modulator,the modulation bandwidth is expected to be good,and the maximum modulation amplitude is also close to 20 dB.But in the dynamic test,when the modulation rate is0.1GHz,a good modulation effect can be obtained,and the modulation depth is close to90%.However,the modulation depth decreases rapidly after the modulation speed is raised.After modulation speed reaches 1GHz,the modulation depth falls to 10%,Further design improvements are needed.The terahertz high-speed waveguide modulator is expected to be developed and applied in terahertz communication,medical imaging,security inspection,radar,telemetry,aerospace and other fields.