| 摘要 |
PURPOSE:To suppress the deformation of a core by heating and the deterioration in a loss characteristic by forming a thin-film layer by a low-temp. CVD method, then heating this thin-film layer, thereby annealing the thin-film layer. CONSTITUTION:A core layer 24 which consists mainly of SiO2 and has a relatively high refractive index is formed by a flame deposition method on an under clad 22 which consists mainly of the SiO2 and has a relatively low refractive index. The core layer 24 is then subjected to pattern etching to form the core 24' of a prescribed shape. The thin-film layer 26 mainly consisting of the Sin. is formed by a low-temp. CVD method on the under clad 22 so as to cover the outside surface of the core 24'. The thin-film layer is annealed by heating and an outer clad 28 which consists mainly of the SiO2 and has the refractive index equal to the refractive index of the under clad 22 is formed by a flame deposition method on the thin-film layer 26. Then, the possibility of generating bubbles in the thin-film layer 26, etc., is eliminated at the time of forming the outer clad 28' by heating and vitrifying. |
