Analysis of elemental distributions and phase separation in rare-earth-doped silica-based fiber preforms and optical fibers

Abstract The elemental distribution, phase separation and nanocrystallization process in rare-earth-doped silica-based fiber preforms and optical fibers were studied by using analytical electron microscopy. The particular properties of devitrification processes depending on the fiber core compositions and concentration of rare earth elements was systematically studied in aluminophosphosilicate fibers. It was investigated that the record high (for Modified Chemical Vapour Deposition manufactured samples) concentrations of rare-earth ions (up to 3 at% Yb3+) can be achieved alongside with a reasonably low background optical losses using aluminosilicate glass matrix. Two types of phase separation were revealed in the investigated samples of different composition: the droplet separation and the formation of two interpenetrated glass phases. It was concluded that the second type phase separation can be accompanied by the formation of nanocrystalline inclusions. Possible applications of the obtained glasses in practice for creation of highly-absorbing layers in optical fibers were discussed in the paper.