Density and concentration fluctuations in a erbium-doped fiber amplifiers glass: Raman and small angle X-ray scattering study

Light scattering in glasses is due to inhomogeneities described as density fluctuations and concentration fluctuations. Both fluctuations are characterized by fictive and chemical fictive temperatures, Tf and Tf′ respectively. A SiO2–Al2O3–P2O5 fiber amplifier glass doped with Er3+ is studied. From Raman scattering the fictive temperature of a fiber is determined to be 130 °C higher than in a preform. In situ small angle X-rays scattering (SAXS) measurements on a sample with an initial fictive temperature of 1100 °C show a structural relaxation below Tg and no evidence of evolution of concentration fluctuations up to 1400 °C. These measurements demonstrate that in a strong glass such as that considered in this work, Tf and Tf′ can be monitored separately allowing a high Tf′ favouring the dispersion of the doping ions and a low Tf decreasing the Rayleigh scattering and increasing the transmission of the signal.