Distributed measurement of gas pressure dynamics in as-drawn hollow-core fibres

After fabrication, the gas pressure inside the core and cladding of hollow-core fibres is significantly below atmospheric pressure. If such an "as-drawn" fibre is then exposed to the atmosphere, pressure-driven flow will push gas from the surrounding environment into the core and cladding holes at different rates, affecting its performance. We use optical time-domain reflectometry to study the length-distributed gas flow dynamics in an as-drawn double-nested antiresonant nodeless fibre (DNANF). For the first time, we show measurement of the initial "as-drawn" pressure distribution along the fibre length and its subsequent evolution over time. Experimental measurements are then compared with gas flow simulations, to enable prediction of pressure equalisation times.