Design of Hollow-Core Anti-Resonant Fibers Supporting Few Weakly Coupled Polarization-Maintaining Modes

A nested semi-tube hollow-core anti-resonant fiber (HC-ARF) that can support the high-purity transmission of a few polarization-maintaining modes is designed in this paper. By employing bi-thickness hybrid silica/silicon anti-resonant tubes, the birefringence of the orthogonal polarized modes is significantly improved, and the weak coupling condition of the five lowest-order polarization maintaining modes, including the LP01_x, LP01_y, LP11a_x, LP11b_x, and LP11a_y, can be met. The effective refractive index difference between each pair of the supported adjacent modes is larger than 1.0 × 10−4. With hybrid multi-layer nested semi-tubes, the confinement losses of the supported modes are all less than 1.50 × 10−1 dB/m within a transmission band from 1.530 to 1.620 μm. The minimum confinement losses of the LP01_y, LP01_x, LP11a_y, LP11a_x, and LP11b_x modes are 3.71 × 10−4 dB/m, 1.61 × 10−3 dB/m, 2.00 × 10−2 dB/m, 1.30 × 10−1 dB/m, and 4.20 × 10−2 dB/m, respectively. Meanwhile, the unwanted higher-order modes are filtered out well to guarantee the modal purity. The minimum higher-order-mode extinction ratio of the lowest-loss LP21 mode to the highest-loss LP11 mode remains larger than 139 from 1.545 to 1.615 μm. The numerical results highlight the potential of the proposed polarization-maintaining few-mode hollow-core anti-resonant fibers in many application fields, such as short-range and high-capacity data transmission networks, fiber sensing systems, quantum communication systems, and so on.