Spectroscopical studies of the ionizing-radiation-induced damage in optical fibers

The results of extensive studies of the attenuation and Raman spectra of all silica (AS), plastic clad silica (PCS), and hard clad silica (HCS and HCR) fibers are presented. A broadband fluorescence centered around 658 nm was observed in the unirradiated fibers and HCR fibers exposed to a dose of 35 rad. The intensity of this band was found to decrease and broaden with irradiation. Another band around 629 nm was observed to increase in intensity with irradiation. The 1350 cm-1 peak to the Raman spectra, observed by Lan et. al. in both boron- and phosphorous-doped fused silica fibers was originally assigned to boron and phosphorous-doped fused silica fibers was originally assigned to boron and phosphorous dopants even though there is some evidence that it is not present in glasses containing a high concentration of these dopants. Results suggest that this peak might be due to the interaction of chlorine with boron or phosphorous dopants. The presence of chlorine in some fibers is not now thought to be responsible for the 1350 cm-1 peak, which is absent from the Raman spectra of high-purity silica fibers with high-chlorine concentrations (HCR type fiber). The analysis of attenuation spectra of 'pure' silica fibers indicated that the spectral differences are unlikely to be due to differing OH concentrations alone and that the different manufacturing processes also play a part. A broadband absorption around 625 nm was observed in a high OH-content fiber receiving 105 Rad dose and is thought to originate from non-bridging oxygen hole center (NBOHC) defects.