Direct measurement of 248-and 193-nm excimer-induced densification in silica-germania waveguide blanks

The densification of a waveguide blank of composition 14GeO(2):86SiO(2) pro duced by 193- and 248-nm excimer exposure was measured by an interferometri c technique. With the aid of a finite-element model, we derive the unconstr ained densification from the experimentally determined optical phase shift. The densification versus exposure can be fitted to a power law and is comp ared with the behavior of fused silica. Again, with the finite-element mode l, an estimate is made of the refractive-index change that would be produce d in a single-mode fiber. For the exposure levels typically used for the 24 8-nm exposure, the densification contribution to the optical index change i s found to be negligible for this composition. On the other hand, for the h igh 193-nm exposure, the densification contribution can be dominant. (C) 19 99 Optical Society of America [S0740-3224(99)00310-0].