Non-Invasive Real-Time Characterization of Hollow-Core Photonic Crystal Fibres using Whispering Gallery Mode Spectroscopy

Single-ring hollow-core photonic crystal fibre (SR-PCF), consisting of a ring of thin-walled glass capillaries surrounding a central hollow core, can offer remarkably low transmission loss [1], and is finding applications in, e.g., wavelength conversion and pulse compression in gases, high-power beam delivery and circular dichroism [2]. As with all microstructured fibres, it is highly desirable to continuously measure the internal structural parameters (e.g. the capillary diameter) during fibre drawing. This would improve the yield of useful fibre lengths, as well as offering better control of structural uniformity along the fibre. Successful tapering of hollow-core fibres also requires a non-destructive method of verifying structural integrity along the taper.