TOPAS-based high birefringence and low-loss anti-resonant hollow-core fiber

This paper proposes a terahertz anti-resonant hollow-core fiber (HC-ARF) using cyclo-olefin copolymer (COC, TOPAS) as the fiber material. The fiber consists of four symmetric nested circular tubes placed along the <i>y</i> axis, two quasi-elliptical tubes distributed vertically, and a central structure composed of dual support pillars and an elliptical air core to further enhance asymmetry. This design achieves low transmission loss while significantly increasing birefringence, thereby ensuring stable polarization state propagation. The structure was analyzed using the finite element method, and the optimized parameters achieve, at 1 THz, a birefringence of up to 3.1×10^-2. The confinement losses of the X-polarized mode and Y-polarized mode are as low as 1.46×10^-6<i>d</i><i>B</i>/<i>c</i><i>m</i> and 2.81×10^-6<i>d</i><i>B</i>/<i>c</i><i>m</i>, respectively, while the material absorption losses are only 2.23×10^-4<i>d</i><i>B</i>/<i>c</i><i>m</i> and 1.53×10^-3<i>d</i><i>B</i>/<i>c</i><i>m</i>. These results demonstrate excellent transmission characteristics, indicating strong potential for applications in future terahertz communication systems.