Research On Terahertz Hollow-core Waveguide Based On 3D Printing Techniques

Terahertz has become one of the hotspots in the current research field due to its special spectral position and potential important applications.This paper first introduces the development and application of terahertz technology,and focuses on the research progress of terahertz polymer waveguide in terms of transmission loss.The development of low-loss terahertz waveguides is one of the solutions to this problem,because terahertz waves are susceptible to the influence of surroundings,such as water vapor in the air,when transmitted in free space.Terahertz waveguide is an important functional component of terahertz communication system and terahertz devices such as detection and imaging.To achieve high efficiency and low loss transmission of terahertz wave is of great theoretical significance and practical value to the development of Terahertz technology.The terahertz hollow waveguide based on the Bragg structure has a good confinement ability to the mode field,can effectively confine the terahertz wave transmission in the air core,and has the advantages of low transmission loss and wide operating bandwidth.However,hollow Bragg waveguide usually needs to be mechanically supported by introducing a support structure in the air ring,which will destroy the band gap structure of the waveguide and induce large confinement loss,resulting in the actual transmission loss much higher than that of the ideal structure.To reduce the influence of support elements on waveguide transmission loss,a terahertz hollow Bragg waveguide with an axial periodic bridge structure is proposed.Based on the analysis of the influence of the Bragg type terahertz waveguide,a structure with bridges on only one ring of air in the cross section of the waveguide is proposed to reduce the confinement loss of the waveguide.In order to support the dielectric layer effectively,discontinuous supporting bridges are used along the waveguide axis and the waveguide units with different air rings are cascaded.The structure of the waveguide breaks the traditional way that the supporting bridge distributes continuously along the axis of the waveguide and reduces the damage of the supporting bridge to the band gap structure of the Bragg waveguide.The influence rule of supporting bridge on the waveguide transmission loss is simulated and analyzed by finite element method.Results show that the supporting bridges in the first air ring play the most important role on the transmission loss.By reasonably selecting the length ratio of the waveguide units,the waveguide absorption loss can be reduced to less than0.4 d B/m in a wide bandwidth range from 0.53 to 0.73 THz and the transmission loss can be less than 0.5 d B/m,which is very close to the result of the ideal structure.On this basis,the photosensitive resin is selected as the waveguide material,and the optical properties of the material are measured by experiment.Then the waveguide of 50 mm length is designed and fabricated by 3D printing technology.The terahertz hollow Bragg waveguide is tested by terahertz time-domain spectrometer.The results show that the waveguide loss is less than 1d B in the frequency range from 0.415 to 0.466 THz.The experimental and simulation results are in good agreement on the transmission loss characteristics.Finally,the design of Terahertz hollow Bragg waveguide based on anti-resonant waveguide structure is proposed,and the waveguide parameters are further optimized and improved to achieve low loss transmission of1.59 d B/m at 0.5THz frequency.