Ultrafast infrared laser fabrication of fibre Bragg gratings with a phase mask

This thesis details the first successful phase mask assisted inscription of a retro-reflecting fiber Bragg grating (FBG) with an ultrafast laser source. Ultrafast FBG fabrication is demonstrated in the traditional Ge-doped silica fiber, pure silica fiber, and sapphire crystal fiber. Successful grating fabrication in pure silica and sapphire indicates that, unlike with traditional UV sources, a wide range of materials can be modified with ultrafast laser radiation.;Hydrogen loading of standard Ge-doped SMF-28 fiber is shown to reduce the grating formation threshold significantly. The existence of two ultrafast induced grating types is demonstrated and their annealing and scaling behavior is investigated. As the index change profile of phase mask assisted ultrafast gratings differs from their UV induced counterparts a Rouard's method model is developed to model the spectral response of these gratings. The spectral response is shown to be consistent with the higher nonlinear intensity dependence of the induced index change. In addition a saturable growth rate is demonstrated and the impact of the incomplete overlap of the induced index change with the core region of the fiber is considered.;A multiple beam interference model is developed that can accurately simulate the femtosecond and picosecond pulse induced interference patterns in the cladding and core regions of the Ge-doped silica fiber. The model is then extended to simulate pulse propagation through the phase mask and investigate the overlap of the diffracted orders. It is found that at extended distances from the phase mask the diffracted orders no longer overlap, resulting in a pure two-beam interference pattern as the +/-1 orders contain most of the incident energy. These predictions are then compared with experimental observations.