Photonic crystal fibres (PCFs) are special fibres with air holes which run along the whole fibre length. These holes not only determine the fibres' unique properties, but also provide a new degree of freedom for fibre modications. In this thesis, we focus on hole control in PCFs from two perspectives: during their fabrication and after they have been made. We found for the first time that the direct information of viscosity was not necessary for description of the fibre drawing process. This conclusion matched our experimental results without recourse to any adjustable fitting parameters. By post-processing of PCFs, which modifies the cladding and core structure and shape, we have achieved a series of novel devices for both linear and nonlinear applications. We have demonstrated fibre devices with cores resembling Young's double slits that have good performance in terms of compatibility and intensity enhancement for a specific application in fibre optic spectrometers. The bulk of this thesis reports on higher-order modes and their nonlinear applications. We achieved all-fibre, low loss and broadband mode converters in highly nonlinear PCFs (HNPCFs) which converted the fundamental mode (LP01) to a higher-order mode (LP02), which can then be converted back if necessary. This higher-order mode has been used for supercontinuum (SC) generation and four wave mixing (FWM) at wavelengths unobtainable for the fundamental mode. This is achieved by utilising the profound dispersion properties of the higher-order mode. We also demonstrated another kind of mode conversion: from the fundamental mode to a Bessel-like beam or its Fourier transform version, an annular beam. Three different methods were implemented experimentally to achieve this non-diffractive, self-healing beam.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:616649 |
| Date | January 2014 |
| Creators | Chen, Yong |
| Contributors | Birks, Timothy ; Wadsworth, William |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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