Gas-induced differential refractive index guidance in hollow-core optical fibers

Hollow-core fibers (HCFs) are a potentially transformative fiber technology, where light is confined within a hollow core surrounded by a cladding composed of air holes defined by glass membranes. Dramatic reductions in the minimum losses achieved in a HCF are driving forward their application in low-latency data transmission and ultra-high-power delivery, and maximizing their performance is of increasing interest. Here, we demonstrate that introducing an extremely small gas-induced differential refractive index (GDRI) between the gas within the core and cladding regions of a HCF enables dramatic changes to a HCF’s optical properties, including loss, bend loss, and modality. Within this work, we focus on a tubular HCF and demonstrate through experiment and simulations that the confinement loss of this fiber can be reduced by a factor of 5 using a differential pressure of only 6.7 bar. Understanding GDRI is critical for applications where the gas content within the fiber is actively controlled. Moreover, GDRI provides a new means to control the optical properties of a HCF post-fabrication, opening up new areas of design space and providing a tool to tailor and enhance the optical performance of even state-of-the-art HCFs.