Highly Birefringent Anti‐Resonant Hollow‐Core Fiber with a Bi‐Thickness Fourfold Semi‐Tube Structure

Abstract The optical performance characteristics of anti‐resonant hollow‐core fibers (known as AR‐HCFs or ARFs) are improving rapidly, but the polarization maintaining issue with these fibers remains unresolved. Although a regular nonbirefringent ARF can maintain high polarization purity under static conditions, it cannot resist mechanical disturbances. In this work, by designing a bi‐thickness semi‐tube ARF structure with fourfold rotational symmetry, the first ARF with a level of birefringence close to 10 −4 is fabricated. The proposed ARF features a combination of phase birefringence of 9.1 × 10 −5 , a minimum loss of 185 dB km −1 , a bandwidth of 133 nm, and single‐mode operation. Furthermore, the ARF shows high resistance to fiber bending and wide‐range temperature variations, thus confirming that this carefully designed ARF can serve as a practical workhorse in polarization‐related optical fiber applications.