Photosensitive glass integrated optical devices

Photosensitive glasses for applications in integrated optical devices have recently become a popular research topic, due primarily to the success of the germania doped silica fibre counterpart. Whole ranges of devices could in principle be fabricated utilising the photosensitivity phenomenon, from directly written waveguides to more complex grating structures. A key parameter in all applications is the change in material refractive index after light exposure. Considerable effort has been devoted to understanding mechanisms responsible for the phenonema with attempts to maximise the effect. To date index changes achieved are ~ 10 -3 which is sufficient for the production of highly efficient holographic gratings within a waveguide, but not quite large enough for direct waveguide formation. Various writing schemes have been developed, but most are based on UV laser sources operating in the 240 - 270nm wavelength range to coincide with a germanium related defect absorption. High quality gratings, with reflection efficiencies of 14dB have been written. These gratings have been used as feed back elements in external cavity lasers and when incorporated in a Mach-Zender interferometer, a channel dropping filter has been demonstrated. With continued effort, more compact optical devices utilising gratings and the photosensitivity effect can be expected in parallel with the fibre development work.