Research On The Novel THz Waveguide

Terahertz electromagnetic waves have broad application prospects in ultrafast process detection, materials characterization, environmental monitoring, object imaging, medical diagnostics, high-speed optoelectronic devices and broadband mobile communication. However, due to the lack of low-loss and low dispersion THz waveguide, its application has been limited to some extent. So research and development of high-performance THz waveguides is important for developing a range of potential applications.This thesis analyzes the transmission characteristics of THz metal hollow waveguide and metal coated hollow waveguide, discusses the factors that affect the transmission characteristics and improves the waveguide by adding a dielectric layer outside the metal film. The numerical results show that the new structure can offer a possibility to design high performance THz waveguide.First of all, the general hollow waveguide is analyzed and the transmission mechanism of metal hollow waveguide is discussed. The first three low-order modes in THz hollow waveguide are TE₁₁, TM₀₁ and TE₂₁ modes. Among those modes the TE₁₁ mode has the longest cut-off wavelength being the main mode in the circular waveguide. The TM₀₁ mode is the lowest order of symmetric mode.Secondly, electromagnetic field simulation software Ansoft HFSS is introduced. Exact solution of mode field distribution, attenuation constant and dispersion of THz hollow metal waveguide is analyzed by the use of HFSS which based on finite element method. The results are concord with the theoretical results. This proves HFSS a feasible and effective method for the study of THz waveguides.Thirdly, the transmission characteristic and structural design of metal coated hollow waveguide are discussed. The impact of core radius, type of coating metal, film thickness, and bending radius are discussed. The optimized structure parameters of THz metal coated hollow waveguide are the inner diameter of 1mm and silver film thickness of 0.1μm. Attenuation coefficient of the main mode of this structure decreases to 2dB/m at 0.5-0.8THz, and the dispersion is less than 1.7ps/THz/cm which meets the demands of transmission on meter level.Finally, the structure of THz metal coated hollow waveguides is improved by adding a dielectric layer outside the metal film. The dielectric/metal hollow waveguide has lower attenuation constant and dispersion compared with metal coated hollow waveguides. The materials and thickness of dielectric layer are discussed to get a better performance. In this waveguide structure, the main mode-TE11 has the attenuation constant of 0.41dB/m, when the thickness of PE layer comes to 13μm. And the dispersion of this waveguide is almost the same as that of metal coated hollow waveguide. In this thesis, the method of choosing the materials and thickness of dielectric layer is given which has laid a good foundation to further improve THz waveguide performance.