It is now well known that fused silica optical fiber can suffer from enhanced strength degrathtion after prolonged exposure to
aggressive environments. This is caused by corrosion of the glass surface by moisture leading to roughening, strength loss,
and, potentially, problems with handleability. It has been found that addition of nanosized silica particles to the polymer
coating can improve the long term mechanical reliability by slowing corrosion and delaying the onset of strength loss.
However, previous studies have shown that addition of these particles can lead to unacceptably high added optical loss, when
measured using the "basketweave" test. In this work, it is shown that the added loss caused by coating additives can be
reduced by improving the mixing and dispersion ofthe silica powders in the polymer. It is further shown that well dispersed
powders still substantially improve the long term fatigue and aging behavior. This clearly shows that coating additives can
improve the mechanical reliability without significantly degrading the optical performance.
Subcritical crack growth in fused silica can be modeled as a stress assisted chemical reaction between water and strained bonds at the crack tip. The stress influences the crack growth rate by reducing the free energy of the activated complex. In principal, the stress changes both the activation enthalpy (energy) and entropy; however, the influence of stress on entropy has generally been ignored. The dynamic fatigue behavior of `pristine' optical fiber can be used to determine the fatigue kinetics parameters with unprecedented precision. It is shown that the entropy contribution is at least as significant as the enthalpy and therefore should not be ignored.
The mechanical reliability of optical fiber used in certain biomedical applications is extremely important because failure of the fiber during use might be fatal for the patient. Therefore, prediction of the lifetime of the fiber both in storage and during service is necessary before the fiber can be safely used. In this paper we study two commercially available optical fibers designed specifically for high power laser delivery. The fatigue parameters calculated from static fatigue data are used to estimate the maximum allowed stress that ensures survival for the deign life of the fiber. This work properly accounts for uncertainty in the predictions; uncertainty which arises not only from scatter in the experimental data, but also from uncertainty in the form of kinetics model to use for extrapolation (i.e. power law, exponential, etc.). This paper thus provides an outline for making lifetime predictions for a critical applications involving relatively short lengths of fiber, that does not bind in any questionable assumptions.
Hermetic aluminum-coated fused silica fibers can withstand high stress levels without failure for prolonged periods of time in water-containing environments. Aluminum-coated fibers from several sources exhibit differences in strength. The aluminum and silica surfaces have been examined using SEM and AFM in order to understand this variation. Differences in the interfacial interaction between aluminum and glass and in the microstructure of the coatings were considered, but were not unequivocally identified as being responsible for the differences in strength observed for the various aluminum-coated specimens.
Conference Committee Involvement (1)
Reliability of Optical Fiber Components, Devices, Systems, and Networks II