METHOD FOR MAKING AN OPTICAL FIBER PREFORM

摘要

In order to solve the above-mentioned problem, a method is provided for the manufacture of an optical fiber preform that is suitable for producing a low attenuation optical fiber with high yield. The method comprises a step of preparing a core rod and a step of adding a cladding region. At the step of preparing a core rod, the core rod is produced including a first core region 21 with a Cl concentration of less than 600 atomic ppm, a second core region 22 with a Cl concentration of less than 600 atomic ppm around the first core region, and a third core region 23 with a Cl concentration of 3000 atomic ppm or more around the second core region, wherein an alkali metal is selectively added to the first core region among the first, second, and third core regions. At the step of adding a cladding region around the core rod, a cladding region 30 is formed around the core rod by heating at a temperature of 1200°C or higher for 7 hours or less.