The Local Polarization Properties of Bent and Twisted Antiresonant Hollow-Core Fibers

Hollow-core antiresonant optical fibers (ARFs) have emerged as a contender to succeed standard solid-core single-mode fibers. Their polarization properties are of primary importance for the operation of polarization-sensitive optical systems. Appropriate models are therefore required to design ARFs that can deliver light with precise polarization performance. This work proposes a method based on coupled-mode theory to extract the local polarization properties, in terms of birefringence and dichroism, of bent and twisted ARFs. The method is applied to a 5-tube nested antiresonant nodeless hollow-core fiber (NANF), and the results are discussed, introducing a model for the behavior of birefringence and dichroism as a function of bending radius and twist rate. Once birefringence and dichroism are obtained, their model can be used to study the polarization evolution and the polarization-dependent loss of ARFs, where the equations involved are the same as those of standard fibers. The proposed method is not limited to bend and twist, and can be applied to any perturbed ARFs where the propagation is effectively single-mode.