Optical properties of long photonic crystal fibre tapers

Abstract

In this thesis I investigate optical properties of metre - long tapers. Microstructured optical fibre technology has created new opportunities in a broad range of science and technology. In the work presented in this thesis I have combined the microstructured optical fibre technology with a novel tapering facility in order to develop new applications in the field of nonlinear optics. This thesis concerns development of a novel tapering facility, capable of achieving intermediate length (few tens of cm to ~10 m) tapers. In comparison with systems presented to date, the novel system has the advantage of the increased control over the desired taper profile and enables efficient fabrication of intermediate taper lengths of potentially arbitrary profiles. During the fabrication the fibre diameter exhibits significant variations, due to various disturbances. A design of the feedback loop for the enhanced control of the output diameter variation is proposed. The system capabilities have been tested and demonstrated in many different examples. The presented results show that the variation of the fibre diameter is within ~1%, which offers possibilities to use the system in various applications. As an example of the intermediate taper length design and application, parabolic pulse generation was investigated. It represents a very attractive pulse shape, since it can propagate at high peak powers while avoiding wave-breaking effect and have a flat and broad spectrum, which could lead to pulse compression applications. This thesis presents numerical modelling and experimental results (restricted to a set of parameters of fibres available from ’stock’) concerning this phenomena. Supercontinuum generation is an area of research that has been attracting scientific interest over several decades. This thesis shows results of a study of supercontinuum generation in intermediate length tapered microstructured optical fibres. A simulation tool has been developed and the procedure to efficiently determine optimum conditions for improving flatness of the supercontinuum spectra has been proposed. The proposed method concerns a ’standard’ microstructured optical fibre, but generally can be extended to different fibre designs.

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