Selectively SF ₆ -filled conjoined-tube hollow-core fibers for low-loss, bend-resistant LP ₁₁ mode transmission at visible wavelengths

We report the design, fabrication, and characterization of a selectively SF 6 -filled conjoined-tube hollow-core fiber (CTF) that enables low-loss (0.45 dB/m at 660 nm), bend-resistant LP 11 mode transmission in the visible range. Numerical simulations and experimental measurements jointly reveal the modal dynamics and bending resilience critical for practical deployment. The fiber achieves high LP 11 mode purity over 36 m, with an LP 01 -to- LP 11 loss ratio of 24.5:1, minimal polarization dependence, and resistance to macro-bending. Distributed side-leakage radiometry and spatially and spectrally resolved (S 2 ) imaging confirm sequential modal filtering along the fiber. This work demonstrates a scalable platform for higher-order mode guidance at visible wavelengths, with potential applications in nonlinear optics, quantum photonics, and light–matter interactions.