Creating large anisotropy in amorphous germanosilicate glass using a novel optical engineering approach

As the demand for novel devices grows in telecommunications, there is a need to generate more flexibility in the materials that will enable these devices to come to fruition. By adding germanosilicate, there is now a range of UV and mid-IR laser processing techniques which are used to fabricate components such as Bragg gratings. However, the basis of these processing methods usually involves a change of density in the glass to achieve perturbations in the refractive index which can be accumulated along a waveguide to create a functional component. In the work described, this processing is enhanced by exploiting some of the unique transitional characteristics of glass recently highlighted as being an important factor in UV processing. This novel engineering exploits the fact that there is an effective rollover threshold between type I and type IIa processing with UV light and that it is strain dependent. In this manner the induced anisotropy is significantly larger than would otherwise be possible through simple UV-induced polarisability or geometric index changes. A buried planar waveguide device where stress conveniently already exists as compression on the waveguide core along the TE vector from the substrate is considered.