Study On Terahertz Hollow Waveguides

With the rapid development of terahertz?THz?science and technology,THz transmission,as an indispensable field in THz technology,has attracted more and more attention.Bendable THz waveguide is expected to achieve low-loss transmission of THz waves.The THz hollow waveguide has a simple structure.It has an air core which serves as a transmission medium and has broad application prospects in the THz waveguide transmission field.In this paper,three types of terahertz hollow waveguides are studied theoretically and experimentally,namely metal hollow waveguide,polymer dielectric tube hollow waveguide and metal/dielectric hollow waveguide.For the study of polymer tube waveguides,thin-wall cyclic olefin copolymer?COC?dielectric tube hollow waveguide was designed to achieve broadband THz transmission.The COMSOL Multiphysics and the geometric optical ray model are used to simulate the transmission performance of the hollow waveguide,and the differences between the two simulation methods are discussed.In order to break through the limitations of the traditional dynamic coating method on the thickness and uniformity of the dielectric layer,we put forward the idea of the piston-type controllable coating method and set up the experimental device.The maximum thickness of the dielectric film has been increased to 30-60?m?the maximum film thickness built up by traditional method is around 15?m?,and a COC dielectric tube waveguide for THz broadband transmission was prepared.It is proved that the transmission bandwidth can be increased by adjusting the wall thickness of the COC dielectric tube waveguide.The experimental measurements show that the straight and bending transmission losses can be as low as 0.10 dB/cm and 0.18 dB/cm respectively within the range of 0.75-1.1 THz.In the study of metal hollow waveguides,the transmission mode,loss and dispersion are analyzed theoretically.The transmission test of 300 GHz terahertz waves proves that the metal hollow core waveguide made of silver or copper has relatively low transmission loss,and increasing the inner diameter of the waveguide can reduce the transmission loss.In order to improve the bending performance of the metal hollow waveguide,a flexible ABS plastic base tube has been used to fabricate the ABS silver-plated hollow waveguide.The transmission loss of this waveguide can be as low as 1.82dB/m at 300 GHz.Theoretically,the position of the low-loss transmission window of a metal/dielectric hollow waveguide is related to the thickness of the dielectric layer and the inner diameter of the hollow waveguide.Theoretical loss analysis of the silver/COC dielectric hollow waveguide with the transmission mode of HE₁₁ mode can be as low as 0.03 dB/m at 300 GHz.In addition,the fabrication process of the silver/COC dielectric hollow waveguide has been preliminarily explored,and it is proved that the piston-type controllable coating method can also be used to prepare the dielectric layer of the silver/COC dielectric hollow waveguide.