Polarization-differential loss enabled high polarization extinction in hollow-core fibers

Delivering a well defined state of polarization over hollow-core fibers (HCFs) is pivotal for next generation ultra-stable photonic systems. Yet in all existing HCFs, whether birefringent or not, their polarization extinction ratio (PER) rapidly deteriorates during propagation or under mechanical disturbance, leaving no practical high and stable PER solution. Here, we break this impasse by embedding a polarization-differential loss (PDL) mechanism directly into the cladding architecture. By deliberately phase matching one core polarization to a leaky cladding resonance, the unwanted polarization is strongly attenuated while the orthogonal mode remains low loss, providing passive stabilization that complements birefringence. A 19 µm-core prototype sustains a PER of 30 dB across a 45 nm band after 725 m, with just 8.5dBkm −1 loss on the working axis and a peak PDL of 456dBkm −1 . Reducing the core to 15 µm boosts the PDL to ∼1800dBkm −1 and delivers PER≈40dB over 102 m, exceeding 50 dB within a 5 nm window while remaining stable when coiled to 6 cm radius. To our knowledge, this is the first demonstration of sustainably high PER in near-kilometer-scale HCFs under practical perturbations. PDL-engineered HCFs thus overcome the longstanding polarization bottleneck, opening a scalable path to bend-tolerant, single-polarization fiber links for gyroscopes, coherent laser delivery, and timing networks.