Characterization and effect of hydrogen treatment and UV irradiation on photosensitive sol-gel derived aluminosilicate planar waveguides

Photosensitive Ce3+-doped aluminosilicate planar waveguides have been prepa red by a sol-gel process. The waveguides, which have been characterized usi ng different techniques, appear to be totally amorphous and of good optical quality. The m-lines technique and waveguide Raman spectroscopy have shown that the doping of the guides with Ce3+ ions slows the densification proce ss and that consequently the effect of doping has to be taken into account for the characterization of such materials. X-ray photoelectron spectroscop y (XPS) analysis of the samples has revealed a very high concentration of n onbridging oxygens (NBO) at the surface. To study the mechanisms responsibl e for the photosensitivity of these waveguides, selected samples have been hydrogenated and irradiated with UV light and then analyzed by XPS. Results have shown a strong decrease of the O/(Al + Si) atomic ratio, especially a t the surface of these guides, after H-2 loading and UV irradiation. This d ecrease is correlated with the high concentration of NBO at the surface of the samples and has been interpreted as resulting from the formation of mol ecular water accompanied by the creation of defects in the glass.