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

Abstract

The densification of a waveguide blank of composition 14GeO2:86SiO2 produced by 193- and 248-nm excimer exposure was measured by an interferometric technique. With the aid of a finite-element model, we derive the unconstrained densification from the experimentally determined optical phase shift. The densification versus exposure can be fitted to a power law and is compared with the behavior of fused silica. Again, with the finite-element model, an estimate is made of the refractive-index change that would be produced in a single-mode fiber. For the exposure levels typically used for the 248-nm exposure, the densification contribution to the optical index change is found to be negligible for this composition. On the other hand, for the high 193-nm exposure, the densification contribution can be dominant.