Vibrational spectroscopy and various physical property measurements (density, molar volume and glass transformation temperature) were used to investigate the structural changes that occurred with changes in composition for glasses prepared by standard melting and quenching techniques in the PbO-Bi2O3-GeO2 system. Regions of constant glass transformation temperature (Tg) were noted for these glasses at high GeO2 compositions, as determined from DSC measurements. These results clearly indicated the presence of amorphous phase separation. A model was proposed that could qualitatively interpret both the infrared and Raman spectra, and the molar volume data. At low lead oxide and bismuth oxide concentrations, lead acted primarily as a network modifier while bismuth acted as a mixed network former and modifier. At high concentrations, both lead and bismuth acted as network formers in linking discrete GeO4-units and possibly forming a lead oxide/bismuth oxide portion of the network. The observed results were also interpreted on the basis of Ge-O bonds involving bridged and non-bridged oxygen atoms, and on the basis of a possible change in coordination for germanium from four to six with metal oxide additions.

Chalcogenide glasses of As2Se3−xTex (O<x<3) were made with special care, using very pure raw materials in order to avoid traces of oxygen. From these materials optical fibers were pulled, and the attenuation of CO2 laser light (wavelength λ = 10.6 μm) transmitted through these fibers was measured as a function of the Te content (x). The fiber's surface and cross-section were examined, using both the scanning electron and optical microscopes, and they directly revealed the increase in the concentration of the defects while x was increasing. The influence of the physical and mechanical properties on the concentration of defects was studied by measuring the optical absorption (α) and the microhardness (VH) of the raw materials. Slabs of As2Se3−xTex were made, and in these samples the α, VH, and glass transition temperature (Tg) as a function of x were measured. In the infrared region of the spectra at λ = 10.6 μm, the α in both the slabs and pulled fibers increased, and the VH and Tg decreased with the increase of x. This can be explained by the increase of the concentration of the defects (small crystallites) which appeared during the fiber pulling.

Strength of Ge-Sb-Se UV-cured acrylate coated chalcogenide glass fibers was measured in various environments using specially designed fixtures for testing in tensile and bending modes. The data are analyzed using Weibull statistics. Humid or water immersion initially lowered the observed strength of these fibers, presumably due to corrosion by the moisture which penetrated the semi-porous coating. However, after the glass surface became wetted, there was no evidence of further strength degradation (over 1.5 months of immersion).

A model reaction is proposed which can totally explain formation of the defects detected in SiO2: GeO2 glasses such as E', NBOHC, T-T, bonding, peroxy linkages, and T=O or T(II) species, where T is Si or Ge. The initial reaction is radical decomposition of T-O bonds at high temperatures and the defects are products of the secondary reaction between the initial radical species. The net reaction is expressed as 2TO2⇄2TO+O2, which predicts the dependence of concentration of the radical species on PO2 during processing.

The γ-induced centers in SiO2 glass such as the Si-E' center and OHC were found to be effected by the atmosphere present during melting. In the case of the VAD process, a porous preform rod is sintered to fabricate a transparent preform rod. The generation of defect species could be easily controlled by controlling the atmosphere of the sintering process. Only small amounts of OHC are generated in fibers sintered in Cl2 or H2 atmospheres, and most of the OHC is recovered at room temperature. This indicates the possibility of making fibers which are highly resistant to irradiation. The correlation between the γ-induced loss increase and the formation of these defects was examined.

We have investigated the relationship of precursor defects in as-drawn optical fiber to glass composition and processing conditions in order to understand the radiation sensitivity of doped-core optical fiber. Techniques are reported for improving the radiation hardness of graded-index multimode fibers through reducing the concentration of doping- and processing-induced defects as well as modifying the residual defects in as-drawn fiber. Significant decreases in radiation-induced loss have been observed for fibers pretreated with hydrogen. An investigation of the role of drawing-induced defects indicates that a lower draw temperature produces slightly harder fiber. A study of core/clad interfacial stress revealed that such stress does not play a major role in radiation sensitivity.

Measurement techniques included in situ loss measurements at 850 nm and spectral loss measurements before and after -γ irradiation. In addition, photoluminescence proved to be an effective tool for characterizing specific defect centers. It was found for Ge/P-codoped fibers that the luminescence band at 650 nm attributed to drawing/radiation induced centers has an inverse correlation with induced loss. Previously unreported emission bands have been observed, including one at 720 nm which may be related to fluorine doping.

Effects of the sintering atmosphere for 90SiO2 :10GeO2 preform-rods produced by VAD process were examined. The sintering atmosphere was changed from reducing to oxidizing, and the type and relative concentration of defects were estimated by photoluminescence, UV absorption and ESR absorption. Reducing condition accelerated the formation of defects, because these centers were considered to be the intermediate products of the thermal decomposition reaction of GeO2 which gives rise to reduction of Ge(IV) to Ge(II).

The reaction of H2 with undoped silica core fibers was evaluated by means of “in situ” spectral loss measurements. Drawing induced loss peaks at 0.63 μm decreased rapidly upon exposure to hydrogen. Simultaneous loss increases at 1.39 and 1.53 μm suggest that H2 reacts at nonbridging oxygens and oxygen vacancies created during the drawing process, forming SiOH and SiH. The 1.53 μm SiH peak slowly decayed after its initially rapid growth, indicating that SiH is not thermodynamically stable in silica. The concentration of drawing induced defects is estimated to be on the order of 100 ppb, based on the time required for H2 to diffuse to the fiber core. The appearance of peaks at 1.45 μm suggests that HF is formed by reaction of H2 in the fluorine doped cladding of the fibers.