Research On New Quasi-optical Devices At Terahertz Wave Band

Terahertz is considered to be one of the most promising science and technology in the 21 st century.In recent decades,with the continuous emergence of new materials and new technologies,the development of terahertz technology is also in full swing.Terahertz technology has broad application prospects,including wireless communication,national defense security,non-destructive testing,imaging,astronomical detection,biomedicine and other directions.At present,the development of terahertz technology is mainly limited by the development of terahertz radiation sources.Finding new terahertz sources with high power,high efficiency and miniaturization is the most urgent task at present.This paper mainly uses electromagnetic simulation method to research new terahertz sources.This article works as follows:1.Investigate the structure of the quasi-optical cavity and derive the relationship between the resonant frequency of the quasi-optical cavity and the resonant mode,the distance between the mirrors,and the curvature radius of the mirrors.The conditions for stable oscillation of the quasi-optical cavity and the design method of related parameters of the cavity are studied to prepare for the research of new quasi-optical terahertz wave devices.2.A new 340 GHz quasi-optical diffraction radiation oscillator is proposed.Calculate the eigenmode,resonance frequency and Q value under the single-period model,and study the influence of related parameters on the eigenmode and resonance frequency.The calculation of the beam-wave interaction of the 340 GHz diffraction radiation oscillator shows that at an operating voltage of 2700 V and a current of 0.017 A,the output power of the device is 4.81 W,and the electronic efficiency is about 10.4%.The frequency of the output signal is 340 GHz,and there is a surface wave mode at 303 GHz,and there is mode competition between the two.The bandwidth tuning characteristics of the device is analyzed.The tuning bandwidth is about 4GHz,which meets the design requirements.3.To further increase the output power of the device,a 340 GHz multi-electron beam diffraction radiation oscillator is proposed.The multi-electron beam diffraction radiation oscillator is to use a plurality of electron beams and a high-frequency field to simultaneously perform beam-wave interaction in a cavity to achieve the purpose of increasing output power.The calculation results show that with the number of electron beams increases,the output power of the device increases significantly.For two electron beams,the output power is 8W.The output power of three electron beams is 12.5W,which is higher than that of single electron beam diffraction oscillator.4.A new quasi-optical double-cavity amplifier is researched.In the calculation,the concept of the average value of the electric field is proposed to measure the intensity of the beam-wave interaction of the device.The cold cavity characteristics such as the field distribution,resonance mode,resonance frequency,figure of merit,and S-parameters of the input cavity and output cavity are calculated.By calculating the beam-wave interaction of the new quasi-optical double-cavity amplifier,the results show that when the input signal power is 0.005 W,the operating voltage is 2650 V,and the operating current is 0.04 A,the gain is above 30 dB from 338.8GHz to 339.8GHz.When the operating current is 0.05 A,a gain of 35 dB can be achieved,and the electronic efficiency is 11.8%.While ensuring high gain and high electronic efficiency,further expansion of bandwidth is the direction of future efforts.