OPTICAL FIBER AND OPTICAL FIBER PREFORM

摘要

Provided is an optical fiber with low transmission loss, and an optical fiber preform which is used for obtaining such an optical fiber and in which crystals are not prone to form in the core. This optical fiber is provided with a core that includes the central axis, and a cladding that surrounds the core and has a lower refractive index than that of the core. The core contains an alkali metal element and elemental chlorine. The average concentration of the alkali metal element in the core is 0.1-20 atomic ppm, the average concentration of the elemental chlorine in the core is less than or equal to 800 atomic ppm, and the transmission loss at a wavelength of 1550nm is 0.185dB/km or less.