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Low temperature consolidation of flame-hydrolysis-deposited silica layer for integrated optics application

A flame-hydrolysis-deposited silica layer is produced and consolidated at low temperature as 850°C. The concentration of boron oxide in the layer is measured to be 13∼15 mole %. Such a low temperature consolidation process of the flame hydrolysis deposition (FHD) layer allows hybridization between the RID and chemical vapor deposition (CVD) method. For example, a CVD phosphosilicate waveguide is covered with the FHD highly-boron-doped silica layer and its properties are examined. The upper cladding (to 24 μm) is successfully deposited in one step and showed good filling capability of the gap between the waveguides. The refractive index of this layer is low (1.453) compared to that of the high pressure steam oxide (1.457). Insertion loss of the 32 mm long sample annealed at 1000°C is 1.13 dB and the propagation loss is estimated as 0.1 dB/cm or better.