Design of Weakly Coupled Two-Mode Hollow-Core Antiresonant Fiber With Low Loss

We first design and optimize a hollow-core conjoined-tube antiresonant fiber (CT-ARF) for weakly coupled LP ₀₁ and LP ₁₁ modes transmission. The critical core radii for the weak-coupling condition in the CT-ARFs with 4 to 8 tubes are obtained. Using numerical simulation, we demonstrate that by tuning the glass sheets positions in cladding tubes the confinement losses (CLs) of higher-order modes (HOMs) LP ₂₁ , LP ₀₂ , and LP ₃₁ can be maximized through core-cladding mode coupling. Among the CT-ARFs with 4 to 8 tubes, the 6-tube one is proved to have the lowest CLs and bending losses of LP ₀₁ and LP ₁₁ modes and the highest CL ratios between the undesired HOMs and the two guided modes. In the designed 6-tube CT-ARF, LP ₀₁ and LP ₁₁ modes have low CLs in the transmission band of 1.31-1.65 μm. The minimum CLs of LP ₀₁ and LP ₁₁ modes are 1.7 × 10 ^-4 dB/m and 3.1 × 10 ^-3 dB/m in the C-band (1.53-1.565 μm) respectively. A 10 cm bend has a weak influence on the two guided modes. The CL ratio between the lowest loss HOM and LP ₁₁ mode keeps >150 in the wavelength range from 1.25-1.65 μm, which ensures the high purity of LP ₀₁ and LP ₁₁ modes. The fabrication tolerances of the fiber are discussed.