Nonlinear properties of silicon core optical fibres

摘要

Silica optical fibres are renowned for the framework they have set in modern communications systems, sensors, and biotechnology. One particular trend in current research aims to investigate materials with enhanced optical functionality, high optical effciency, robustness, and a small device footprint. Amongst the many material choices, semiconductors are emerging as a promising route. In this work, optical fibres and semiconductors are elegantly unified to create a hybrid structure with the potential of seamless integration into current fibre infrastructures. Silica capillaries form the fibre templates in which amorphous semiconductor materials such as silicon and/or germanium are impregnated. This thesis will present the first comprehensive description of the fabrication, characterisation, and the implementation of silicon optical fibres for all-optical signal processing. The fibres are fabricated via a novel high pressure chemical deposition procedure. Each fibre is analysed to determine the exact material composition, uniformity, and more importantly the optical quality. Linear and nonlinear optical characterisations are performed experimentally and supported by intensive numerical studies to validate the results.The high nonlinearity of silicon is exploited for all-optical signal processing. Several investigations have been performed to determine key nonlinear coeffcients that were previously unknown in these fibres. Nonlinear absorption experiments allowed for the determination of the degenerate and non-degenerate two-photon absorption coeffcients, free carrier cross sections, and free carrier lifetimes of a number of silicon fibres. Nonlinear refraction investigations were then used to establish the Kerr nonlinearity. The strength of this parameter allowed for demonstration of strong self-phase and cross-phase modulation effects. With the insight gained in nonlinear absorption and refraction in silicon optical fibres, all-optical amplitude modulation and wavelength switching was demonstrated at ultrafast sub-picosecond speeds.