Defect centers induced in GeO2 glass by either 100-KeV x rays at 77 K or γ rays at room temperature were studied by electron-spin resonance. The model of a singly charged oxygen vacancy defect center for the Ge E′ center (g∥ =2.0012, g⊥ =1.9945) was confirmed by the observation and computer simulation of the 73Ge hyperfine structure associated with this center. The evolutions of the Ge E′, peroxy radical, and nonbridging oxygen hole centers were studied by isochronal thermal annealing. Surprisingly, the Ge(2) center, a defect previously known only in Ge-doped silica, and an additional center with a hyperfine coupling constant half that of the Ge E′ center were found in pure GeO2 samples irradiated at 77 K; these, too, were studied by isochronal thermal annealing and computer simulation. Structural models for these centers are presented.

Refractive index dispersion has been determined for fluorine doped fused silica containing 1 and 2% fluorine. Addition of fluorine is found to reduce the refractive index and material dispersion. Fibers modeled for minimization of modal dispersion having fused silica cores and fluorine doped silica cladding show a strong composition dependence of the optimum refractive index profile. Comparison of results with those in the literature based on N.A. vs λ measurements reveal minor discrepancies probably due to the drawing process.

Defect centers induced by ionizing radiation (50–100-keV x rays, 60Co γ rays) in high purity P-doped silica glass have been observed and elucidated by ESR spectroscopy. Four generic species are well characterized on the basis of the observed 31P hyperfine splittings and g values as defects analogous to PO2−3 (phosphoryl), PO4−4 (phosphoranyl), PO2−2 (phosphinyl), and PO2−4 radicals. The latter species, also termed the phosphorus-oxygen-hole center (POHC), is shown to occur in two variants comprising holes trapped on one or two nonbridging oxygens. Radiation-induced Si E′ centers with and without P next-nearest-neighbors were also identified, and a singlet resonance S due to E′ type defects such as (OSi2)Si⋅ and/or (O2Si)Si⋅ was observed to grow in with annealing above ∼800 K, regardless of whether or not the sample was irradiated. The structures, formation mechanisms, and precursors of these defects have been determined or inferred for all centers. Radiation-induced optical absorption spectra over the range 0.5–6.2 eV have been obtained for bulk glass and fiber samples after irradiation and following anneals to various temperatures up to 1250 K. Gaussian resolutions of the spectra into component bands have been performed and isochronal anneal data have been used to identify optical absorptions of the PO2−3, PO4−4, PO2−2, POHC, and S centers. The PO2−3 defect was found to absorb at ∼0.8 eV in the region of interest for fiber optic communication. Oscillator strengths are calculated for all bands.