Phase Separation and Crystallization of Phosphate–Silicate Glass Cores of Preforms of Fiber Optics

Abstract—The phase separation and the emergence of nanocrystalline inclusions in phosphate–silicate preforms for optical fibers activated with ytterbium, which are obtained by the powder sintering methods with the vibrational mixing of the melt and the addition of ytterbium-containing nanoparticles into preforms, are studied. Nanocrystals of YbPO₄, SiO₂, and YbP₃O₉ are formed in the preforms in the low-temperature areas of the powder sintering process when using either of the methods. It is concluded that the phosphates are crystallized as a result of the phase separation from the glass phase enriched with ytterbium.