Generation and manipulation of short optical pulses in fibre based systems
This thesis presents experimental and computational work on a variety of fibre based systems covering the generation, transmission, manipulation and amplification of short optical pulses (hundreds of femtoseconds to tens of picoseconds). The construction and characterisation of an all-polarisation-maintaining fibre figure-8, passively mode-locked laser is presented. This was the first all-fibre passively mode-locked cavity constructed entirely of high birefringence, polarisation maintaining components. This enabled the generation of a single polarisation Eigen-state within the cavity, resulting in a source of high quality 2.3ps-6ps solitonic pulses with excellent environmental stability, despite the considerable length of the device (395m). A computational model of a dispersion compensated standard fibre link using a fibre based four-wave mixing, midpoint spectral inversion (MPSI) technique was developed to provide qualitative and quantitative support to a 50km experimental system for the transmission of 6ps solitonic pulses. This model was then used to provide an estimate of the limitations to such systems presented by higher order dispersion, the results suggesting that links greater than 2500km at single channel bit-rates of 50GBit/s could be feasible. The development of photorefractive fibre Bragg gratings has produced one of the most important and flexible fibre devices. Experimental and computational investigations of the interaction of short pulses with both uniform and linearly chirped gratings are presented, giving a useful insight into their dispersive effects and limitations for their use in more complex systems. The importance of apodisation for reducing the energy scattering from pulses after multiple reflections was clearly demonstrated through numerical modelling of such systems. The application of long, linearly chirped fibre Bragg gratings to the compensation of chromatic dispersion in step-index fibres at potential bit-rates approaching 50GBit/s was demonstrated experimentally with the transmission of 16ps pulses over 100km. The use of two cascaded 4cm gratings exploited the linearity of these devices to further push the limits of compensation available. One of the few limitations of fibre based short pulse sources is the relatively low pulse energies produced. This problem had been tackled through the use of chirped pulse amplification (CPA) to circumvent the limitations imposed by fibre nonlinearities to amplification in EDFAs, however the problems of energy extraction from the amplifier fibre remained. The development and application to CPA of a large mode-area EDFA designed to improve pulse energy extraction is presented. The generation of 32?J pulses directly from the amplifier represented a significant increase in both energy and pulse quality over previously reported systems, demonstrating the potential of such amplifier designs for a range of high energy/intensity pulse applications.