New optical fibre based technologies and their application in highly nonlinear systems

This thesis investigates new fibre technologies and their application in nonlinear optical systems, designed mainly for telecommunications. The thesis includes a study of two different directions in achieving a high nonlinearity in a fibre system, namely holey fibres filled with nonlinear liquids and soft glass, small core microstructured fibres. The challenges arising from the development of liquid-filled structures have made soft glass microstructured fibres the technology of choice for the realisation of highly nonlinear systems.Amongst the various soft glasses, commercially available lead-silicate glasses are identified as the material for the development of highly nonlinear fibres. Small-core, leadsilicate fibres with different designs are considered within this thesis. A solid core holey fibre design as well as two all-solid designs, a multi-ring cladding and a simpler W-index profile, are characterised. The measurements confirm the advantages of the all-solid designs over the holey structures and reveal the possibility to achieve simultaneously a high nonlinear coefficient and a novel dispersion profile in such fibres. Some of the presented fibres are employed in all-optical wavelength conversion schemes based on four-wave-mixing. Numerical simulations and experimental results are combined to study the performance of the fibres and demonstrate their use in wavelength conversion devices. In particular, a lead-silicate W-index profile fibre, showing a high nonlinear coefficient of 820W-1km-1 with a near zero dispersion profile at telecoms wavelengths, is employed to demonstrate a flat conversion gain in the whole C-band. The same fibre is then employed in FWM-based systems to demonstrate multi-channel wavelength conversion, generation of high repetition rate pulses and all-optical demultiplexing. The experiments presented in this thesis clearly reveal the potential of small-core soft-glass fibres for nonlinear applications.The use of soft glass microstructured fibres in the mid-IR is also investigated. Tellurite holey fibres with different core sizes and hole arrangements are employed in a supercontinuum generation scheme