Cushman Darby & Cushman
Method for fabricating an optical waveguide
 In the first step, a fuel and raw material gases are fed to burner while flames from the burner scan a Si substrate. Synthesized fine glass particles are deposited on the substrate to form a first porous vitreous layer to be an under cladding layer. In the second step, the first porous vitreous layer is heated by the flames. A bulk density of an upper part of the first porous vitreous layer is raised to 0.3 g/cm.sup.3. Having a raised bulk density, this upper part functions as a shield layer against GeO.sub.2. In the third step, a second porous vitreous layer, to be a core layer, is deposited uniformly on the first porous vitreous layer. In the fourth step, the first and the second porous vitreous layers are sintered. In this case, the shield layer with a higher bulk density hinders the GeO.sub.2 component which has evaporated from the second porous vitreous layer from diffusing into the first porous vitreous layer. 
Sumitomo Electric Industries, Ltd.
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Hiroo Shinji Chisai Haruhiko Masahide Akira
Kanamori Ishikawa Hirose Aikawa Saito Urano