理论分析了金属、介质/金属结构空芯光纤在THz波段的模式结构和传输特性。金属空芯光纤支持TE11模式, 介质/金属空芯光纤的介质膜厚在取最优值时支持HE11模式。对于波长为200 μm的太赫兹波, 内径为1 mm的两种空芯光纤, TE11和HE11模式的损耗分别为8.4 dB/m和2 dB/m。为优化介质/金属结构空芯光纤的传输性能, 分析了金属和介质材料的光学常数对衰减系数的影响。基于几种已发表的金属在太赫兹波段的光学常数, 计算结果表明铝是最好的选择; 初步测量结果显示, 在各种树脂材料中聚乙烯在THz波段吸收较小, 并且其折射率接近介质膜的最优值1.41, 为太赫兹波空芯光纤中介质膜材料的理想选择。

Transmission characteristics and mode structure of both metal hollow fiber and dielectric-coated metal hollow fiber for terahertz wave are studied. Theoretical evaluation shows that the TE11 mode is dominant in metal hollow fiber and has high coupling efficiency when a linearly polarized light source is launched. HE11 mode is mainly supported in dielectric-coated metal hollow fiber with an optimum thickness for the dielectric film. The transmission loss of the TE11 and HE11 mode is 8.4 dB/m and 2 dB/m respectively at the wavelength of 200 μm for the hollow fibers with 1 mm bore size. The effects of optical constants of metals and dielectric materials on attenuation coefficient are also discussed to optimize the transmission performance of dielectric-coated metal hollow fiber. Aluminum is the best choice among the commonly-used metals based on published optical constants. The optimum value for the refractive index of the dielectric film is 1.41. According to the primary measuring results, polyethylene is a proper choice as its refractive index is 1.51 and it brings low absorption in terahertz waves.