面向太赫兹波段的负曲率光纤设计及数值研究

文章设计了一种基于环烯烃共聚物（cyclic olefin copolymer，COC）的空芯负曲率光纤（negative curvature fiber，NCF），分析结构参数光纤芯径、管径和毛细管厚度对光纤限制损耗的影响，并对参数进行优化，使得单包层NCF在2.0～2.5 THz频率范围内限制损耗为 $ 10^{-4}\sim10^{-5} $ dB/m，损耗最低值可降到8.90× $ 10^{-5} $ dB/m；引入内包层管破坏常规负曲率光纤的对称性，使纤芯模式与内包层管壁模式进行耦合，从而增加x和y偏振方向的折射率和损耗差异产生双折射；对影响光纤双折射特性和限制损耗的因素进行分析，在2.0～3.0 THz频率范围内双折射系数可达到 $ 10^{-4}\sim10^{-5} $。该文结果为太赫兹NCF的长距离传输、偏振敏感等应用提供了一条新的途径。

A hollow-core negative curvature fiber (NCF) based on cyclic olefin copolymer (COC) is designed. The effects of structural parameters such as fiber core diameter, tube diameter and capillary thickness on the confinement loss of NCF are analyzed, and the parameters are optimized. The simulation results show that the confinement loss of single-cladding NCF is $ 10^{-4}-10^{-5} $ dB/m in the frequency range of 2.0-2.5 THz, and the minimum confinement loss is reduced to $ 8.90 \times 10^{-5} $ dB/m. By introducing the inner cladding tube to destroy the symmetry of the conventional NCF, the fiber core mode is coupled with the cladding capillary mode, which increases the difference in refractive index and loss in the polarization directions of x and y to produce birefringence. The factors affecting birefringence and confinement loss of NCF are analyzed. The birefringence can reach $ 10^{-4}-10^{-5} $ in the frequency range of 2.0-3.0 THz. The simulation results provide a new way for long distance transmission and polarization sensitive applications of terahertz NCF.