Influence of fiber drawing on optical UV attenuation of all-silica fibers with undoped core

Abstract

The appearance of intrinsic defects, especially in the UV spectral range, has been investigated in step-index fibers having undoped silica core and a fluorine doped cladding; the concentration of the dominant impurities ranged from 2 to 50 ppm and from 400 to 600 ppm. The optical attenuation from 190 to 500 nm was not only determined in fibers, but also in the preforms and core rods. The absorption bands at 248 nm, at 340 nm and at 210 nm were observed. While the preform process has no significant influence, the fiber drawing process influences greatly the defects' concentration: the 210 nm band increases slightly, the 248 nm band increases significantly, the 340 nm band decreases. No influences of the fluorine cladding was determined with one exception when the chlorine content has been increased in the cladding of special species. The possible reactions and related defects will be described for the tested low-OH material. Especially the influence of chlorine will be discussed.