Use of selectively buried ion-exchange waveguides for the realization of Bragg grating filters

Ion exchange on glass substrates has proved to be an efficient low cost and high performance technology to realise integrated optic devices. Among structures developed thanks to this technology, those presenting both surface and buried waveguides are of great interest. In this paper, we first describe a fabrication process of selectively buried ion exchange waveguides. Its principle is based on a two step ion exchange process. First a surface waveguide is realised by a thermal exchange of Ag + -Na + . Then a mask is deposited on the back side of the optical wafer perpendicularly to the axis of the waveguide. Finally a second step assisted by an external electric field is performed. Then we report the performances of this method through the measurement of the burying depth evolution. When the mask is wide enough, the burying depth varies from 2 m above the middle of the mask to 12 m in the unmasked region. The transition is 3 mm long and therefore avoid any excess losses. For this structure, no deformation of the fundamental mode has been observed. Finally, the first results of use of these selectively buried waveguides to realize Bragg filters with a surface grating is presented through a comparison of measured reflexion spectra.