| 摘要 |
PROBLEM TO BE SOLVED: To form a refractive index increasing portion of an axially symmetric shape excellent in consistency with an optical fiber, irrespective of a deep embedded depth, using two-step ion exchanging method. SOLUTION: Such three processes are conducted in order as the first ion exchange process for forming an ion exchange controlling membrane on a glass substrate to be immersed into the first molten salt to conduct thermal ion exchange so as to form a refractive index increasing portion, an etching process for removing the ion exchange control membrane, and the second ion exchange process for impressing an electric field to be perpendicular to the substrate while immersed into the second molten salt so as to embed the refractive index increasing portion along a depth direction of the substrate. The first method makes impressed electric field intensity in the second ion exchange process lowered with the lapse of time. In the second method, the third ion exchange process is conducted to impress an electric field reverse-directional to that in the second ion exchange process while immersed into the second molten salt after the second ion exchange process. In the third method, a heat- treatment process is conducted to hold heatingly the substrate under a no- electric-field condition after the second ion exchange process. |
