Hollow core fibres for deep UV guidance

: (Alternative Format Thesis)

Abstract

The transmission of ultraviolet wavelengths through conventional optical fibres has long faced significant limitations due to strong scattering and absorption losses. These inherent challenges are further exacerbated by solarisation, where exposure to ultraviolet light damages the glass matrix and leads to increased attenuation over time. Consequently, standard optical fibres can only support low intensities of ultraviolet light over short fibre lengths. These constraints not
only limit light delivery but also the non-linear generation of ultraviolet wavelengths, that has proven highly useful for visible and near-infrared wavelengths.

Anti-resonant hollow-core fibres offer a promising alternative by guiding light through a gas or vacuum filled core, thereby bypassing material limitations and enabling low loss, damage free ultraviolet light transmission. These fibres rely on precisely engineered glass capillaries, whose wall thickness just a few hundred nanometres thick. As achieving such structural parameters has historically been difficult, only a handful of reported fibres have sufficiently thin and small capillaries for broadband ultraviolet light guidance. The research in this thesis is about the development of fabrication techniques to reliably draw ultraviolet guiding hollow core fibres, and the broader application of those techniques and fibres. A series of hollow core fibres in lengths of 100 - 1000 m are reported for the practical delivery of deep-ultraviolet light (190 - 250 nm), along with studies of various gas absorptions that can block ultraviolet and visible light transmission. Examples of their use for the non-linear generation
of light are presented, including the compact generation of < 15 fs visible light pulses and a supercontinuum spanning 260 - 750 nm in a single fibre. The fabrication of a new class of fibres with ultra-thin (< 100 nm wall thickness) capillaries is presented, and these fibres are used to demonstrate vacuum-ultraviolet light guidance over metre lengths for the first time. Beyond ultraviolet wavelengths, these fabrication techniques were applied to create multi-mode
and multi-core hollow core fibres with improved uniformity and performance. An experimental study of multi-mode guiding fibres is presented, demonstrating highly multi-mode hollow core fibres can be fabricated with low propagation losses and reasonable bend resistance. Their modal characterisation is achieved using established principles of far field analysis, with excellent
agreement between experiment and numerical simulation.

Date of Award	25 Mar 2026
Original language	English
Awarding Institution	University of Bath
Supervisor	Tim Birks (Supervisor) & James Stone (Supervisor)