Patent ID: 10155687

Abstract:
An optical fiber preform of the present embodiment comprises a core portion and a cladding each comprised of silica glass. The core portion has a first dopant region including a central axis of the core portion and a second dopant region away from the central axis. The first dopant region contains a first dopant selected from among Na, K, and their compounds, and a concentration of the first dopant is 10 atomic ppm or more but 2,000 atomic ppm or less. The second dopant region contains a second dopant reducing viscosity of the silica glass. The second dopant has, as a characteristic at a temperature of 2,000° C. to 2,300° C., a diffusion coefficient of 1×10−12 cm2/s or higher but lower than that of the first dopant, and a concentration of the second dopant region is 10 atomic ppm or more.