Structure and Mechanism of Formation of Drawing- or Radiation-Induced Defects in SiO2:GeO2 Optical Fiber

Abstract

The structure, mechanism of formation and thermal reaction of electronic defects associated with Ge in GeO₂-doped silica fiber induced by fiber-drawing or γ-irradiation were studied by detecting ESR hyperfine structures due to ⁷³Ge. The present assignment of the drawing-induced center to the Ge-E' center was confirmed from the estimated spin density on a 4s atomic orbital of ⁷³Ge(\cong30%). The radiation-induced center was found to have a larger spin density on a ⁷³Ge-4s orbital(\cong35%) than the drawing-induced center, and in the structural model proposed for the center, the unpaired electron is trapped on a GeO₄ group (Ge electron trapped center: GEC). Most of the GECs induced by γ-irradiation at 77 K were bleached out by annealing at RT in dry fibers, while some of the GECs changed into Ge-E' centers in irradiated GeO₂-SiO₂ glass containing a considerable number of OH groups.