AbstractCreating optical fibres which transmit ultraviolet (UV) wavelengths is challenging due to the material absorption and photodarkening effects of silica glass, the most commonly used material in optical fibres, at these wavelengths. Previous studies have managed to guide down to deep-UV wavelengths (> 200 nm) using a hollow-core negative curvature fibre (HCNCF) to evade the material absorption of glass. The research presented here further develops this type of optical fibre by creating the first multimode HCNCF where it was found that the number of guided modes scales faster with core area than that of a solid-core step-index fibre. The goal was to guide vacuum-UV wavelengths (< 190 nm) for space-based applications. The results were successful such that a multimode hollow-core negative curvature optical fibre was manufactured which was shown to guide wavelengths down to 135 nm through the antiresonant effect and as far
as 110 nm through glancing angle reflections.
Due to the success of the hollow-core negative curvature structure in the vacuum-UV it was conjectured that a similar performance would be seen at other extreme wavelengths, specically 10 micrometers. The issues at this wavelength is similar to that in the UV where the loss is dominated by the material absorption of glass. To combat this, current optical fibres which guide this wavelength have their core-cladding boundary coated with a metal and are cylindrical in shape. The research concluded that a metal-coated hollow-core negative curvature fibre had a greater loss than its hollow-core metal-coated cylindrical fibre counterpart. However, it did provided insights into the guiding mechanisms which makes a hollow-core negative curvature fibre low loss at shorter wavelengths.
|Date of Award
|11 Oct 2021
|William Wadsworth (Supervisor) & Tim Birks (Supervisor)