OPTICAL FIBER AND OPTICAL FIBER PREFORM

摘要

PROBLEM TO BE SOLVED: To provide an optical fiber having a low transmission loss, and an optical fiber preform which is used for obtaining the above optical fiber and substantially prevents crystallization in a core.SOLUTION: The optical fiber includes a core and a cladding that encloses the core and has such properties that: the core contains alkali metal elements and chlorine elements; an average concentration of the alkali metal elements in the core is 0.1 atomic ppm or more and 20 atomic ppm or less; an average concentration of chlorine elements in the core is 800 atomic ppm or less; and the fiber shows a transmission loss of 0.185 dB/km or less at a wavelength of 1550 nm.