Transient differential pressure-induced loss variation in as-drawn hollow core optical fibres

Abstract

We demonstrate transient changes in the optical properties, specifically the loss, of antiresonant hollow core fibres (HCFs) due to a combination of the sub-atmospheric gas pressure inside the fibre holes post-fabrication and the subsequent gas-induced differential refractive index (GDRI) between the core and cladding elements of the fibre; this is temporarily created while the gas pressures inside the core and cladding elements are evolving after the HCF ends are opened up to surrounding atmospheric pressure. Here we show experimental evidence of this effect in two different HCF designs; for both fibres, the transmitted power initially increases, reaches a maximum, and then reduces to its initial level. We show via gas flow simulations that the timeline of this behaviour is consistent with the gas flow rates into the core and cladding elements of the tubular HCF studied and the subsequent transient differential gas pressure. The experimental results also show (in line with GDRI expectations) that this transmission (loss) change is higher at shorter wavelengths. Our results imply that this transient change in the fibre’s optical properties must be considered for accurate fibre characterisation; this is particularly true for long fibre lengths where the equalisation of the fibre’s internal gas pressure with atmospheric pressure could take many weeks.

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Identifiers

ORCID for Peter Horak: orcid.org/0000-0002-8710-8764

ORCID for Yong Chen: orcid.org/0000-0003-0383-6113

ORCID for Thomas Bradley: orcid.org/0000-0001-6568-5811

ORCID for Austin Taranta: orcid.org/0000-0002-5666-6800

ORCID for Francesco Poletti: orcid.org/0000-0002-1000-3083

ORCID for David J. Richardson: orcid.org/0000-0002-7751-1058

ORCID for Natalie Wheeler: orcid.org/0000-0002-1265-9510

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