Comparison of Er-doped sol-gel glasses with various hosts

Using the sol-gel process, we prepared three groups of Er-doped glasses, namely, Er-doped SiO₂-AlO_1.5 (SAE) glass, Er-doped SiO₂-TiO₂-AlO_1.5 (STAE) glass, and Er-doped SiO₂-GeO₂-AlO_1.5 (SGAE) glass. Various erbium concentration and different host composition under the same processing condition have been studied in order to optimize the material composition to get the strongest fluorescence emission for each material system. It has been found that for SAE glass, the strongest fluorescence emission is obtained when the mole ratio of the three constituent oxides is 100SiO₂ : 20AlO_1.5 : 2ErO_1.5. For the STAE material system, the best composition ratio for the strongest fluorescence emission is 93 SiO₂ : 7TiO₂ : 20AlO_1.5 : 1ErO_1.5, whereas the value for SGAE glass is 90SiO₂ : 10GeO₂ : 20AlO_1.5 : 1ErO_1.5. But the relative lifetimes were obtained with the recipe 100SiO₂ : 10AlO_1.5 : 1ErO_1.5 for SAE series, 90 SiO₂ : 10GeO₂ : 10AlO_1.5 : 1ErO_1.5 for SGAE group and 93 SiO₂ : 7TiO₂ : 20AlO_1.5 : 1ErO_1.5 for STAE group. Using these recipes, three 20-layer (up to 2.5 μm) crack-free films have been deposited on silica-on-silicon (SOS) substrates with multiple spin-coating and rapid thermal annealing (RTA). Only the STAE film and the SGAE film are found to guide light. The experimental results show that STAE glasses have higher hydrophilicity than SGAE glasses and SGAE glasses has lower crystallization temperature than STAE glasses. The fact that these waveguiding films emit relatively strong fluorescence around the wavelength of 1.55 μm implies that such planar waveguides are potential candidates from which integrated optical waveguide amplifiers and lasers operating at the third optical fiber communication window can be fabricated.