A silica planar waveguide structure, where a ridge waveguide resides on a vacuum gap, was invented. The silica layer, which was fabricated through thermal oxidation at 1150 °C, had an excellent optical index uniformity on the order of 3×10-5 @1550 nm, and a thickness uniformity of 10 nm at a thickness of 10 µm. Straight waveguide with low insertion loss was demonstrated. Improved thermal efficiency of this structure to cause phase change was discussed in comparison to the conventional channel waveguide structure. Finally, the limitation of this technology to make complex device structures was also explored.
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