Abstract
By exploiting the strain-related rollover thresholds that occur between UV-induced positive and negative index regimes in germanosilica glass it is possible to engineer large anisotropy into the structure. This is qualitatively analyzed for a planar waveguide and has been confirmed experimentally. However, the technique described here is not confined to waveguide devices and can in principle be applied to any glass structure that is capable of undergoing strain-sensitive transitions.