Birefringent, low loss, and broadband semi-tube anti-resonant hollow-core fiber

We report on the design, fabrication, and characterization of a low-loss birefringent semi-tube anti-resonant hollow-core fiber (AR-HCF). By optimizing the structure design and the stack-and-draw fabrication technique, a transmission loss of 4.8 dB/km at 1522 nm, a <10 dB/km bandwidth of 154 nm, and a phase birefringence of 1.8 × 10-5 are demonstrated. This achieved loss is more than one order of magnitude lower than the previously reported birefringent AR-HCF and the bandwidth is one order of magnitude broader than the reported birefringent photonic bandgap hollow-core fiber (PBG-HCF) with the same loss level. The polarization extinction ratio (PER) reaches the ∼20 dB level in a 90 m-long fiber under >25 cm bending radius. Combined with the single mode and low dispersion features, the developed semi-tube AR-HCF may find a variety of applications in frequency metrology, interferometric fiber gyroscopes, and long-baseline stellar interferometry.