Birefringence And Internal Stress In Pzg Fluoride Glass Planar Waveguides

The internal stress of fluoride glass planar waveguides grown by vapour phase deposition have been estimated from birefringence measurements. It is found that the strong anisotropy does not arise from a thermal expansion mismatch but more from internal stresses that develop as the vapour is quenched on the heated substrate. The evolution of stress against substrate temperature and thermal annealing are analysed. The anisotropy is thought to be caused mainly by structural relaxation of the glass.