Irradiation of Optical-Fibre Blanks as a Test of Impurity Content and Radiation Sensitivity

The effect of cobalt-60 gamma rays on doped silica preform rods (optical-fibre blanks) has been studied. Using high doses and short lengths of rod, the local variations od dopant impurity concentration in chemical-vapour deposited (CVD) silica layers on silica can be made visible as stratified colorations, while the presence of unintentional impurities is also made visible. This novel finding may possible be used in predicting the degree of sensitivity to radiation to be expected in optical fibres drawn from silica or glass rods and should be particularly useful in characterzing impurity profiles in advanced designs made by the multilayer CVD process. Preliminary measuremnts indicate that the abosrption spectra of the rods are consistent with those observed at lower doses in drawn fibres.