Scanning near-field optical microscope characterisation of microstructured optical fibre devices
This thesis details work relating to the characterisation of microstructured fibres using SPM techniques. More specifically the optical properties of the fibres have been investigated by the use of a scanning near-field optical microscope and atomic force microscopy. The SNOM was constructed and fully characterised as part of this work. The current state of research into microstructured fibre fabrication, theory and applications is currently benefitting from a great deal of interest from academia and commercial investors alike. New fibre structures are being produced at a rate previously impossible. With this increase comes a need to be able to characterise more effectively the fibres that are produced. SNOM provides a number of significant features that address this issue. In this work four recently fabricated microstructured fibres have been investigated at a number of wavelengths. In each case accurate mode pro- files have been measured and compared with resolution that would be extremely difficult to obtain with traditional mode profiling techniques. A theoretical model has also been used to predict the mode profiles. Measurements of the mode profiles after propagation in free space are presented and are compared to a theoretical beam propagation technique. An interferometric technique at 1550nm was used to image electric field amplitude and phase of the fibre modes, including results on the phase evolution of the mode as it propagates in free space.