Research Of Low Loss THz Waveguide Based On High Molecular Compound

The terahertz frequency range is from0.1THz to10THz, wavelength is from30um to3mm.THz wave has some unique advantages, for example, low energy, water absorptioncharacteristics, strong penetration, etc. So it is very important for medical imaging、chemistry、biological and other fields. Because water vapor absorption and atmospheric scattering have agreat effect on terahertz signal, they can not make long-distance transmission, so the study ofterahertz waveguide is very important for developing terahertz pulses applications. While, atpresent, when the developed THz waveguides transmit terahertz, both the transmission loss andscattering are very serious, complex structure, high cost, and they all can not make long-distancetransmission. Therefore, it has a very practical application value to study a THz waveguidestructure with a simple structure, low-cost, low-loss and long-distance transmission.This paper mainly describes the circular hollow-core waveguide structure of polymercompound material, the structure is based on the principle of anti-resonant reflection, theadvantage of the molecular compound material in doing terahertz waveguide is discussed, wetheoretically study the effects of the hollow tube waveguide attenuation loss factors, using finiteelement analysis method simulates the relationship among structural parameters of the medium,refractive index of the material, terahertz frequencies and the attenuation loss. Through theexperiment verify the reliability of simulation conclusions. By experiment we find that thepolymer compound teflon material with low-loss characteristics when transmits terahertz waves.Through changing structural parameters of the medium, refractive index of the material,terahertz frequencies, we can get a THz waveguide with the lowest attenuation loss.The specificwork as follows:Firstly, through the analysis of terahertz waveguide design, the transmission mechanism andthe attenuation loss formula of hollow-core tube waveguide is introduced, the HE11mode has the lowest cut-off frequency, so it is the main mode of the circular waveguide. The advantage of themolecular compound material in doing terahertz waveguide is discussed, namely, hightransparency、low dispersion and low loss for THz waves, good flexibility, low cost, maturetechnology and other advantages. Using finite element analysis method simulates modalintensity and electric field vector distributions of the first four low-orders modes of a variety oftransmission modes in the circular waveguide, we get the propagation constant of several modelsin the simulation results, then analyze their attenuation coefficients, and comparing with thetheoretical value which proves the feasibility of the simulation software Comsol.Secondly, when terahertz waves transmit in the hollow tube waveguide, modal index andtransmission loss of the fundamental mode are discussed. By combining theory and simulation,we know that diameter、 thickness、 refractive index of the dielectric pipe waveguide andterahertz frequencies have great influences on transmission loss, we have found that theattenuation loss decreases as the inner diameter of the tube waveguide increases. The attenuationloss also changes periodically with the thickness and the refractive index of the cladding, theattenuation loss is the maximum under the resonance condition, in contrast, the attenuation lossis the minimum under the anti-resonance condition. According to the above conclusion, we candesign a tube waveguide with the lowest attenuation loss and the best construct.Finally, through software simulation and practical experimental analyze the relationamong diameter、 thickness、 refractive index of the dielectric pipe waveguide, terahertzfrequencies and attenuation constant. When THz frequency is110GHz, the inner diameter of35mm, the cladding thickness of5mm, the material of Teflon is the most reasonable structure. Theattenuation constant has been measured by simulation, which is as low as0.0228m-1, theattenuation loss is reduced to5.84dB/m by experiment.In this paper, we design a low-loss terahertz hollow-core waveguide structure constituted ofpolymer compound material based on the principle of anti-resonant reflection, combiningsoftware simulation with experiment analyze the relation among the structural parameters、refractive index of the dielectric pipe waveguide and attenuation loss, through changing these parameters, we can get a THz waveguide with low-loss.