| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical waveguide coupler which is low in film stress and has high reliability at a good yield as a quartz optical waveguide coupler necessary for multiplexing optical signals in an optical communication transmission system. SOLUTION: A directional coupler and/or Y-branch circuit is formed by an optical waveguide on an optical waveguide 2 and the end of the optical waveguide is formed as a light input/output terminal. Silicon dioxide optical films doped with fluorine are formed as the optical waveguide on the optical waveguide substrate 2 by a plasm chemical vapor deposition method using gaseous TEOS and O2 and glass CF4 in accordance with the controllability of the refractive index of the silicon dioxide optical film by the content concn. of the gaseous fluorine. Three layers; a lower clad part 31, a core apart 32 and an upper clad part 33 are formed by these silicon dioxide optical films. The refractive index of the core part 32 is made slightly larger than the refractive index of the clad parts 31, 32 by lowering the fluorine concn. of only the core part 32 or not introducing the fluorine into the core part 32 alone. |
