Fabrication and optical measurements of germanium-doped silica ridge waveguides using a colloidal suspension approach

Germanium-doped silica ridge waveguides for planar lightwave circuits were fabricated using colloidal suspensions. After consolidation at 1300 °C, fully dense micron-scale thick films were obtained. The refractive index of these films was tuned with germanium dopant up to 11.1 mol %. The propagation loss of a 3.1 mol % germanium-doped silica sample without an overcladding layer was 3.3±0.5 dBcm. Postannealing of the patterned waveguides at 1200 °C for 30 min was conducted in order to reflow waveguides, but it did not significantly smooth the sidewall roughness due to the high viscosity of the 3.1 mol % germanium-doped silica at that temperature.