METHOD OF MANUFACTURING OPTICAL FIBER PREFORM AND OPTICAL FIBER PREFORM

摘要

The present invention relates to a method of manufacturing an optical fiber preform for obtaining an optical fiber with small transmission loss. A core preform included in the optical fiber preform has at least three core portions each produced with a rod-in-collapse process and in which both an alkali metal element concentration and a chloride concentration are independently controlled. In at least two of the manufacturing processes of the manufacturing processes of each of the at least three core portions, an alkali metal element is added. As a result, an average value of the alkali metal element concentration in the whole core preform is controlled to 7 atom ppm to 70 atom ppm.