Single-polarization single-mode hollow-core anti-resonant fiber with nested stadium-shaped tubes.

A single-polarization hollow-core anti-resonant fiber (HC-ARF) with nested stadium-shaped tubes is proposed for single mode, low loss, and high birefringence characteristics. X-pol fundamental mode (FM) is coupled to the cladding mode (CM) by introducing four anti-resonant tubes and one resonant tube. Y-pol FM is tightly bound in the fiber core, thus achieving a high polarization extinction ratio (PER). In order to achieve a large bandwidth, a silicon layer was coated on the inner surface of the cladding tube, and by optimizing the structural parameters of the silicon-coated HC-ARF, HC-ARF for single-polarization single-mode transmission with high order mode extinction ratios (HOMERs) of 530 and PERs of 15,135 were obtained at 1.55 µm. In addition, single-polarization bandwidths up to 220 nm, birefringence levels higher than 10, and an ultra-low confinement loss (CL) of 5.0 × 10 dB/km have been achieved. The fiber has good bending characteristics, with a minimum bending loss of 0.52 dB/km at a bending radius of 4.0 cm in the y-direction and a minimum bending loss of 3.5 dB/km at a bending radius of 5.7 cm in the + x-direction. Structural deviation occurs during the actual manufacturing of fibers, and the structural deformation tolerance of fibers is evaluated for the purpose of the actual manufacturing of fibers.