Ultraviolet light induced refractive index structures in germanosilica

The focus of the research presented in this ph.d. thesis is refractive index structures photoinduced in germanonsilica waveguides with ultra-violet (UV) radiation. The physical mechanisms involved in photosensitivity and applications of a wide range of UV induced refractive index structures in both optical fibers and planar wavguides have been explored. This work includes fabrication of fiber Bragg gratings and design of equipment intended for enhancement of photosensitivity by indiffusion of molecular hydrogen. New insight regarding UV induced reactions in germanosilica has been provided through application of a scanning near-field optical microscope to obtain high resolution images of UV induced refractive index structures and by monitoring the dynamics of UV induced index changes and luminescence. During part of my ph.d. project I have worked at the National Institute of Standards and Technolgy in Colorado (USA) under supervision of Dr. Sarah L. Gilbert, fabricating and characterizing erbium doped fiber lasers incorporating UV written Bragg gratings. Due to their compact structure, such devices are shown to exhibit a frequency stability several orders of magnitude better than lasers incorporating bulk optics. Finally, I have developed a new method for direct UV writing of planar waveguide devices using a focussed continuous wave UV laser beam which is scanned across a photosensitive thin film deposited on a silicon wafer. Contrary to other waveguide fabrication techniques this method requires no additional wafer processing. By demonstrating a wide variety of integrated devices it is shown that the performance of this method in terms of waveguide loss, flexibility and fabrication yield rivals or surpasses that currently obtainable with other more elaborate techniques.