OPTICAL-FIBER PREFORM AND METHOD FOR MANUFACTURING OPTICAL-FIBER PREFORM

摘要

An optical fiber preform which can be drawn into a low attenuation optical fiber is provided. An optical fiber preform 1 is provided with a core portion 10 and a cladding portion 20 surrounding the core portion 10. The core portion 10 includes a first core portion 11 and a second core portion 12 surrounding the first core portion 11. The cladding portion 20 includes a first cladding portion 21 surrounding the second core portion 12 and a second cladding portion 22 surrounding the first cladding portion 21. The first core portion 11 contains an alkali metal element, the concentration of oxygen molecules contained in glass is 30 mol ppb or more and 200 mol ppb or less in a part of or entire region having an alkali metal atom concentration of 100 atomic ppm or more, and the concentration of oxygen molecules contained in glass is 10 mol ppb or less in a region having an alkali metal atom concentration of 50 atomic ppm or less.