A theoretical study into the fundamental design limits of devices based on one- and two-dimensional structured fibres
The sub-wavelength perturbation of an originally uniform material in order to manipulate light is the basis of two of the latest key technologies used to produce optical fibre devices for telecommunication system applications. The first technology (fibre Bragg gratings) concerns the 1-dimensional perturbation of the refractive index of an optical fibre (i.e. along the propagation axis of the fibre), whereas the second technology (microstructured optical fibres) concerns a 2-dimensional perturbation of the refractive index (i.e. in the transverse plane of the fibre).Regarding the fibre Bragg gratings, the effect of background losses on uniform gratings and of cladding mode losses on linearly chirped gratings have been studied by means of two extended versions of coupled-mode theory. The possibility of compensating the cladding mode losses acting on the chirped grating profile is also analysed. Considering the microstructured optical fibres, an extensive study of highly nonlinear, small-core, silica holey fibres has been performed with the implementation of the multipole method, which was chosen after a careful consideration of other available modelling techniques. Guidelines were produced for optimising the design of holey fibres for particular device applications especially when trade-offs between small effective mode area and low confinement loss are important. The work on modelling highly nonlinear holey fibres was extended to include a preliminary study of the use of higher refractive index glasses and their future device applications.