Design of terahertz fibers using polymer tube bundles and their guided mode and propagation loss analyses

Flexible terahertz fibers were designed for terahertz wave applications. In this paper, new terahertz fiber structures using polymer tube bundles were proposed. A triangle structure fiber with three-tube core and a hexagonal structure fiber with mono-tube core were considered. Mode field distributions in the proposed terahertz fibers and their propagation losses were numerically calculated using the finite element method. It was found that lower propagation loss was obtained for longer operating wavelength and smaller thickness of polymer tube due to the fraction increment of electromagnetic field propagating in the air. It was also clarified that lower propagation loss was brought by introducing the core tube material with lower absorption coefficient, where the propagation loss increased for longer wavelength due to the electromagnetic field expansion into the cladding region with larger absorption coefficient compared with the core material. •New terahertz fiber structures using polymer bundles were proposed.•A three-tube core structure and a mono-tube core structure were considered.•Mode field distributions in the proposed fibers were numerically calculated.•Propagation losses in the proposed fibers were theoretically estimated.•The conditions for low propagation losses were clarified.