Abstract

UV photosensitivity in planar waveguides has primarily concentrated on the generation of sufficient oxygen-deficient centres using germanosilicate glass. There exists a wide range of methods fo fabricating such glasses, all with varying degrees of photosensitivity. Empirically, in planar waveguide at least, the degree of photosensitivity seems to be closely related to the defect induced losses such a increased Rayleigh scattering. For example, waveguides fabricated using flame hydrolysis exhibit very low propagation losses indicating a high level of purity of the glass. Consequently, this material requires sensitisation with hydrogen in order to achieve sizeable index changes with uv irradiation [1]. On the other hand, recent developments have allowed the demonstration of ultra-strong Bragg gratings in unsensitised PECVD-based glass [2], although at the expense of significantly higher propagation losses. A somewhat more impressive demonstration of photosensitivity has been the demonstration of direct waveguide writing with a mercury lamp in organically-derived glass using sol-gel methods [3]. By incorporating organic components into the glass silica polymer matrix, index change is achieved through polymerization of the organic ends which is a substantially different mechanism to that relying upon oxygen deficient centre absorptions. Low propagation losses, whilst maintaining a large photosensitivity, have been achieved this way. In addition to these materials, strong uv photosensitivity has also been observed in ion beam implanted material, mainly with Si²⁺ and Ge³⁺ implanted germanosilicate glass [4,5] although some work has been reported on changes in the uv spectra of H⁺ implanted germanosilicate waveguides [6].

© 1997 Optical Society of America