AlPO₄ in Silica Glass Optical Fibers: Deduction of Additional Material Properties

A silica clad optical fiber with a core comprised of SiO₂, P₂O₅, Al₂O₃, and AlPO₄ is analyzed in order to determine the impact of AlPO₄ when added to silica. A chromatic dispersion curve is presented, from which the nonlinear refractive index is estimated to be similar to that of silica. When doped into SiO₂, AlPO₄ decreases the thermo-optic coefficient (slightly), decreases the acoustic velocity, broadens the Brillouin spectral width through increased viscoelastic damping, and reduces the strength of the dependence of Brillouin frequency on temperature. Findings herein indicate that AlPO₄ has a near-zero value of p₁₂. It also is found that the fiber does not have complete AlPO₄ formation, with some P₂O₅ formation in Al₂O₃-rich regions of the fiber. Given the relevance of AlPO₄ to high power active fiber technology, the presented data can be used for designing fibers with enhanced performance characteristics, such as those with elevated threshold for the onset of stimulated Brillouin scattering.