First Triple Nested Antiresonant Nodeless Hollow Core Fiber (TNANF) Achieving 0.25 dB/km Loss with Small $145/250 \mu \mathrm{m}$ Glass/Coating Diameters

We report an improved antiresonant hollow-core fibre with triple-nested tubes to minimise loss at SMF-type $250 \mu \mathrm{m}$ coating diameters. When MFD-matched to SMF, the fibre has 0.54 dB/km and record bend-loss performance. Increasing its MFD by $\sim 30 \%$ produces 0.25 and 0.35 dB/km at 1550 and 1310nm, respectively. © 2025 The Authors