The Research On Terahertz Metasurface Modulators

In recent years,terahertz communication technology has developed rapidly.However,the lack of high-performance core devices limits its development.The terahertz modulator is the core component of the terahertz communication system,and the improvement of its performance plays a vital role in the development of terahertz communication.In order to solve the problems of low modulation depth and low modulation rate in the research of terahertz modulators domestic and abroad,the HEMT-based terahertz modulator has been systematically studied through theoretical analysis,design simulation,processing testing and experimental research.In addition,a high-performance electronically controlled terahertz modulator has been realized.The proposed modulator has the ability to modulate the amplitude of the terahertz wave in the vertical and horizontal polarization directions,as well as a certain phase modulation ability.This paper focuses on the following research work:Firstly,the research background and current research status of the terahertz metasurface modulators has been introduced.The existing problems of the metasurfacebased terahertz modulators has been summarized.Secondly,based on the theory of metasurface and the working principle of HEMT devices,the design methods of HEMTbased terahertz modulators were proposed.Based on the method above,two HEMT-based electronically controlled terahertz modulators with "symmetric bridge" and "4C split ring" structure respectively were designed.The transmission coefficient spectrum of the two modulators with the varied two-dimensional electron gas concentration in the HEMT channel were studied according to the Drude model.The working mechanism of the two modulators were analyzed.The influence of the changing parameters of the modulator structure on the device performance were discussed.Then,the "4C split ring" type metasurface modulator which provides better performance was processed.The mask of the modulator was drawn,and the modulator chip was fabricated and packaged.Finally,the "4C split ring" type metasurface modulator was tested.On the one hand,by testing the I-V characteristic of the "4C split ring" modulator,it was verified that the modulator has the characteristics of Schottky diodes.On the other hand,a terahertz time-domain spectroscopy system and a terahertz dynamic test system based on external modulation were built to test the modulating ability of the modulator driven by DC voltage and sinusoidal AC signal,respectively.The test results show that: when the incident electric field is in the vertical direction,the modulation depth of the modulator is 57%,with the phase modulation capability of 0.58 rad,and the modulation rate is 200 MHz;When the incident electric field is horizontal,the modulation depth of the modulator is 50%,with the phase modulation capability is 0.72 rad and the modulation rate is 94 MHz.In summary,the modulators designed in the thesis have good performance,which have important potential applications in the fields of terahertz communication and terahertz imaging.