Single-polarization low loss Terahertz Hollow-Core Anti-Resonant Fiber with high Polarization Loss Ratio

We proposed a single-polarization low loss Terahertz (THz) Hollow-Core Anti-Resonant Fiber (HC-ARF) with 4-tube nested Semi-Elliptical Cladding Tubes (SECTs). Through adopting different wall-thicknesses of SECTs along two orthogonal directions, single-polarization and low loss performance can be simultaneously achieved by means of mode coupling between X-polarized Fundamental-Mode (FM) and dielectric mode of SECTs. By optimizing structural parameters, Polarization Loss Ratio (PLR) of X-polarized FM to Y-polarized FM reaches up to 156 at the frequency of 0.5 THz. As a result, only single Y-polarized FM can effectively propagate through the fiber with a low loss of 0.98 dB/m at 0.5 THz. Meanwhile, single Y-polarized region with PLR ≥ 20 covers the frequency range from 0.484 THz to 0.517 THz, i.e. frequency bandwidth of 33 GHz, thus a wide single polarization bandwidth can be obtained. To the best of our knowledge, the proposed THz HC-ARF has the highest PLR, low-loss and relatively wide bandwidth among currently reported THz HC-ARFs. In addition, this THz HC-ARF has been confirmed to have good manufacture tolerance and excellent SP frequency tunability.