Wideband and ultra-low confinement loss nested hollow-core anti-resonant fiber with double-single-layer structuresErlei Wang, Qiang Wang, Quan Cheng and Xiaodong ZhouEur. Phys. J. D, 78 10 (2024) 133DOI: https://doi.org/10.1140/epjd/s10053-024-00926-3