UV-photosensitivity and refractive index engineering in silica-based planar lightwave circuits

Similarly to optical fibers silica-based planar waveguides can exhibit the property of photosensitivity when illuminated with UV light. UV-induced changes of refractive index in Ge-doped silica allow for adding new functionality to these components including wavelength filtering with help of Bragg gratings, phase adjustment, wavelength tuning, direct UV-writing of waveguides and birefringence compensation. Bragg gratings imprinted in waveguide core in the same way as done in fibers, allow for building demultiplexers, add-drop filters, dispersion compensators, frequency lockers and other grating assisted devices. In this paper we present the background of the photosensitivity in germanosilica, methods for its improvement as well as technology for fabrication of advanced low dispersion Bragg gratings for 40 Gbps and beyond. We also demonstrate some fabricated wavelength selective devices for WDM communication systems.