Design of weakly coupled few-mode hybrid nested-single tube anti-resonant fiber with low loss

• Design a hybrid nested-single tube anti-resonant fiber with few-mode transmission. • The new fiber enhancing mode restriction and suppressing gap modes. • Adaptability innovation between "high-performance design and mature fabrication. In this work, we design a hybrid nested-single tube anti-resonant fiber (HNST-ARF) with few-mode transmission characteristics, aiming at solving the problems of high higher-order mode loss and significant mode crosstalk in conventional hollow-core fibers. After optimization of the structural parameters, the low-loss transmission of LP 01 , LP 11 and LP 21 modes can be supported in the range of 1–1.3 μm, with the LP01 confinement loss as low as 4.46 × 10 −7 dB/m, and the confinement losses of the higher-order modes are all lower than 0.001 dB/m. It supports low-loss transmission of LP 01 and LP 11 modes in the range of 1.3–1.37 μm. The effective refractive index difference between modes is always greater than 1 × 10 −4 , which satisfies the weak coupling condition between modes and can effectively suppress inter-mode crosstalk. Further comparative analysis shows that the synergistic effect of gap single-layer tube and symmetric double inner tube design can effectively suppress the cladding leakage and gap mode coupling. In addition, HNST-ARF with a bending radius of 10 cm or larger have less impact on the transmission performance of HNST-ARF with fewer modes, and the mode capacity can be dynamically regulated by wavelength selection. This study provides theoretical support and design examples for the application of hollow-core fibers in mode division multiplexing (MDM) systems and high-capacity optical communications.