Defect structure of glass and its impact on linear and nonlinear optical communications

The propagation of light in glass optical fibers can be affected in many ways by the presence of defects. A convenient working definition of a defect in a glass is any local atomic arrangement which differs from an idealized continuous random network (CRN). For a pure silica glass, the idealized CRN would find each Si tetrahedrally bonded to four O's and each O bonded to two Si's. An oxygen vacancy on the O sublattice is perhaps the most familiar prototype for such a defect in SiO2.1 A certain number of these vacancies, together with some form of O interstitial, are thought to be present in any real silica glass as Frenkel defects. The concentrations of Frenkel defects in silica and silica based glasses are influenced by the methods of glass preparation and the types and concentrations of dopant introduced, e.g., for the purpose of index modification. Some of the dopant associated defects in as-prepared silica based fiber optic glasses are electrically charged and diamagnetic, while most defects which are quenched into pure silica glasses are electrostatically neutral and diamagnetic. These precursor defects generally absorb light in the UV or vacuum UV.