Optical fiber and method for producing optical fiber preform

摘要

An optical fiber having a central axis includes a core extending along the central axis and containing an alkali metal element, and a cladding having a lower refractive index than the core, wherein a radial distance with respect to the central axis is defined as r, a power of light propagating through the core at the radial distance r is defined as P(r), and a fictive temperature at a radial distance r max at which rP(r) becomes maximum is at least 50°C lower than a fictive temperature on the central axis. The fictive temperature profile can be obtained by having a maximum alkali metal concentration at distance r max . A method of making the core preform comprises doping with an alkali metal element the inner surface of a glass pipe, inserting a glass rod into the doped glass pipe and collapsing the glass pipe on the rod to form a core portion.