Study Of Terahertz Anti-Resonant Polymer Waveguide

As the applications of terahertz (THz) technology continue to increase, low propagation loss and low bending loss waveguides are seen as key technology for enabling a more convenient delivery of THz light. Given the finite conductivity of metals and the high absorption loss of dielectrics of traditional waveguides, it appears that a viable solution for low loss propagation and low bending loss is the hollow polymer waveguide, and the THz wave can propagate along the inner air core of this kind of waveguide. Such waveguide offer not only the potential for low propagation loss and low bending loss, but a suitable fiber design can also induce an effectively single mode waveguiding regime.In this thesis, we have explored a feasible method of THz polymer fiber design by Comsol Multiphysics software, which is based on the wave equation and boundary conditions. At the same time, the transmission characteristics of the anti-resonant waveguides in terahertz regime are analyzed by numerical simulation. Meanwhile, by using THz-TDS, the transmission broadband spectral properties of SiO2waveguide, single mode pipe waveguide and self-supporting waveguide are studied, which proves the existence of anti-resonant phenomenon. Based on this mechanism, we are trying to use such kind of waveguides on typical material sensing, which provides a new way on material detection. Moreover, we have built a versatile THz-TDS (time domain spectroscopy) setup, which has an adjustable optical path length specially designed for the transmission measurements of waveguides up to50cm in length.The detail works of this thesis are shown as follows:(1) Element method is introduced as numerical simulation method in detail. According to the waveguide propagation theory and the FEM (Finite Element Method) theory, three types of pipe waveguide with different structures are proposed and investigated, by using simulation software Comsol Multiphysics4.3b, such as the calculation of the transmission mode, effective refractive index, attenuation loss of the anti-resonant pipe waveguides. (2) The transmission properties of the waveguides have been discussed. By using self-built waveguide THz-TDS, the transmission broadband spectral properties of SiO2waveguide, single mode pipe waveguide and self-supporting waveguide are studied, which proved the existence of anti-resonant phenomenon. Although there have been theoretical studies on two of the proposing THz polymer fibers (pipe waveguide and self-supporting polymer waveguide), to our knowledge, we present the first experimental realization of such fibers in the THz regime. The properties such as transmission mode, attenuation loss and bending loss are obtained by a self-built CO2terahertz laser waveguide experimental system and theoretical analysis.(3) Based on the anti-resonant mechanism and the relationship between refractive index and the anti-resonant frequency, we are exploring on using such kind of waveguides on typical material sensing, which provides a new way on material detection.(4) We have built a versatile THz-TDS (time domain spectroscopy) setup, which has an adjustable optical path length specially designed for the transmission measurements of waveguides up to50cm in length.In conclusion, the propagation and sensing properties of the anti-resonant polymer waveguides have been studied theoretically and experimentally. The result shows that such waveguides have good transmission characteristics with low attenuation and bending losses. It is confirmed that such waveguides seek for new possibility on delivery of THz light and material sensing.