The fabrication and development of microstructured optical fibres for beam delivery and generation

Abstract

In this thesis I describe my work on the development and fabrication of fibres for beam delivery and generation. In all cases it is assumed the fibres will be suitable for high power applications. I describe the challenges of fabrication and refinements to existing techniques needed to produce and characterise the diverse fibres. Two jacketed air clad (JAC) fibres with square cores are developed. One is a passive delivery fibre that has capacity to capture a larger beam parameter product than other research and commercial fibres and was designed to deliver the output from a 1800W diode source. The second jacketed air clad fibre has an inner core doped with Yb ions and a shaped pump core defined by a large NA air cladding. This gave reduced fibre length in an amplifier (compared to a conventional rare earth double clad fibre) providing an advantage with respect to the onset of non linear spectral broadening. Two all-solid photonic bandgap fibres (S-PBGF) for beam delivery from a fibre laser with a wavelength of 1070nm and simultaneous rejection of stimulated Raman scattering (SRS) light at a wavelength of 1126nm are presented. The fibres gave larger MFD near 1µm with SRS suppression than other published results at the time of this work. A new type of leakage channel fibre, called the micro-clad leakage channel fibre (micro-clad LCF), is demonstrated for the first time. This fibre type is intended for both beam delivery and in future fibres with an inner core doped with rare earth ions, for beam generation. I present the fabrication and characterisation of an exemplar fibre with mode area of 1440µm². A class of simple antiresonant hollow core fibres are investigated. Various single cladding layer fiber structures are examined. I show that the spacing between core and jacket glass and the shape of the support struts can be used to optimize confinement loss. I demonstrate the detrimental effect on confinement loss of thick nodes at the strut intersections and present a fabricated hexagram fibre that mitigates this effect in both straight and bent condition by presenting radially aligned nodes. This fibre has loss comparable to published results for a first generation, multi-cladding ring, Kagome fibre with negative core curvature and has tolerable bend loss for many practical applications.

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ORCID for David Richardson: orcid.org/0000-0002-7751-1058

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