Reduced Loss and Bend Sensitivity in Hermetically-sealed Hollow-core Fiber Gas Cells using Gas-induced Differential Refractive Index

Hollow-core optical fiber (HCF) gas cells are an attractive option for many applications including metrology and non-linear optics due to the enhanced gas-light interaction length in a compact and lightweight format. Here, we report the first demonstration and characterization of a selectively pressurized, hermetically sealed hollow-core fiber-based gas cell, where the core is filled with a higher gas pressure than the cladding to enhance the optical performance. This differential gas pressure creates a gas-induced differential refractive index (GDRI) that is shown to enable significant modification of the HCF's optical performance. Measurements on fabricated gas cells indicate a significant broadband reduction in attenuation of up to ∼10 dB (at 1100 nm) for a 24 m fiber length and an estimated pressure difference of ∼6 bar between the gas in the core and cladding regions. Additionally, using the fabricated gas cells, we show experimentally for the first time that GDRI can reduce macrobend loss in HCFs. Finally, long term (one year) measurements indicate no degradation in the gas cell performance due to gas permeation or gas exchange between the core and cladding regions, demonstrating the viability of using this gas cell format to implement a GDRI within a HCF to improve optical performance over an extended time period in an all-fiber format.