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

We first design and optimize a hollow-core conjoinedtube antiresonant fiber (CT-ARF) for weakly coupled LP01 and LP11 modes transmission. The critical core radii for the weakcoupling 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) LP21, LP02, and LP31 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 LP01 and LP11 modes and the highest CL ratios between the undesired HOMs and the two guided modes. In the designed 6-tube CT-ARF, LP01 and LP11 modes have lowCLs in the transmission band of 1.31-1.65 mu m. The minimum CLs of LP01 and LP11 modes are 1.7 x 10(-4) dB/m and 3.1 x 10(-3) dB/m in the C-band (1.53-1.565 mu m) respectively. A 10 cm bend has a weak influence on the two guided modes. The CL ratio between the lowest lossHOMand LP11 mode keeps > 150 in the wavelength range from 1.25-1.65 mu m, which ensures the high purity of LP01 and LP11 modes. The fabrication tolerances of the fiber are discussed.