Terahertz Matching Technique Of Optical Waveguide Detector

Terahertz wireless communication is generally considered to be the core of the sixthgeneration mobile communication technology,which can greatly improve performance on the basis of 5G technology and help create more application scenarios.However,due to the performance deficiencies of traditional electronics at high frequencies,it is difficult to exert the core advantages of terahertz wireless communications.The photonic terahertz communication front-end uses a photoelectric detector(PD)as a terahertz source,which has better high-frequency performance compared to electronic devices.When the PD is used as a terahertz source,the incident optical signal is converted into an terahertz signal,and then emitted by the antenna.Starting from the PD generating photocurrent to the terahertz signal radiating out through the antenna,the whole transmission and radiation process is directly related to the transmitting power of the terahertz communication front-end module.This involves issues such as photoelectric conversion,impedance matching,feed structure design,and antenna design.Therefore,this thesis conducts the following research to address the above key issues:1.Based on the basic theory of photodiodes,the impedance characteristics of UniTraveling-Carrier Photodiode are studied.Then,a method for calculating the source impedance of PD is proposed.The circuit parameters of PD are obtained through CST and Silvaco ATLAS simulation,by combining the simulation results and photodiode theory,the equivalent circuit model of PD is established,which can be used to analyze and calculate the source impedance of PD.Finally,the source impedance of PD at 340 GHz frequency is calculated as(19.1-j2.0)Ω.2.A theoretical analysis of several common terahertz antennas has been done.The proposal of the antenna integrated with PD is studied,and the lens antenna is determined to be used as the antenna integrated with PD.Based on the simulation results of the PD source impedance,a bow-tie antenna conjugate matched to the PD and a silicon lens for radiating THz signal are designed.At the center frequency of 340 GHz,the gain is about20.0 d Bi,and the relative bandwidth with VSWR less than 2 is about 17.6%.Then,the second proposal is studied,the proposal that the PD is fed to the antenna through the transmission line.The coplanar waveguide output structure of the PD and the tapered slot antenna fed by the coplanar waveguide are designed.At the center frequency of 340 GHz,the gain is about 11.2 d Bi,and the relative bandwidth of the antenna is about 67.1% when the VSWR is less than 2.3.Based on the working principle of microstrip line and rectangular waveguide,a scheme of PD waveguide output module is proposed,which includes microstrip linerectangular waveguide conversion structure,microstrip feed structure and pyramidal horn antenna.The PD waveguide output module is designed by HFSS software,and the VSWR is less than 1.25 in the operating band of 320 GHz-360 GHz,and the antenna gain is about24.3 d Bi at the center frequency of 340 GHz.The back-to-back waveguide verification structure has been designed and tested to verify the performance of the conversion structure.