Enhancing the Optical Properties of Hollow Core Fibre Gas Cells by Selective Core Pressurisation

Low loss light transmission within gas-filled hollow core optical fibres (HCFs) enables enhanced gas-light interaction and has opened up opportunities for novel and diverse applications, including high sensitivity gas detection, spectroscopy, and non-linear optics [1]. In some applications, such as frequency metrology, a compact HCF-based gas cell can provide significant advantages over a conventional bulk gas cell [2]. Several different methods for integrating HCFs into hermetically sealed gas cells have been demonstrated [2], [3]. Usually these HCF-based gas cells have the same gas pressure and composition in both the core and cladding of the HCF. Recently, we demonstrated that by creating a gas-induced differential refractive index (GDRI) via a differential gas pressure between the core and cladding of a HCF, for example, by selectively increasing the gas pressure in the core, the fibre's optical properties (e.g., loss) can be significantly modified [4]. Here, for the first time to our knowledge, we employ this concept in a hermetically sealed HCF-based gas cell. By selectively pressurising the core, we demonstrate an increase in transmission of up to ~ 10 dB at 1100 nm and periodic measurements have so far indicated that this transmission increase is maintained, with no indication of gas permeation or leakage.