Radial distribution and absorption cross section of active centers in bismuth-doped phosphosilicate fibers

Determination of the active centers distribution across the fiber core as well as calculation of absorption cross sections is a challenging task for all types of bismuth-doped fibers. This is due to the low concentration of active centers and the ability of the bismuth ions to form various centers in silica-based glasses. In this work, we demonstrate the results of experimental measurement of radial distribution of bismuth active centers associated with phosphorus in fiber core using the luminescence spectroscopy. The shape of the distribution turned out to have prominent reduction of the active centers in the middle of the core. With these data, absorption cross section spectra were calculated by two methods. Both approaches demonstrated close values of absorption cross sections regardless the bismuth concentration and fiber geometry. The maximum of the absorption cross section was found to be 2.1 ± 0.3 pm².