Mechanical durability of ZBLAN and aluminum fluoride-based optical fiber

Zero stress aging and static fatigue experiments were performed on fluoride glass fibers of ZBLAN and aluminum fluoride-based compositions to examine the mechanical durability in aqueous solutions. ZBLAN fiber, which has the higher initial strength, becomes weaker than initially lower strength aluminum fluoride-based fiber in less than one hour in pH 7 buffer solution at 30°C. This is shown to be due to dissolution of the glass and precipitation of crystals at the glass/coating interface. In 1N NaOH the solubility is higher, resulting in less precipitation and hence less strength degradation. Although ZBLAN fiber degrades more quickly when a high strain is applied, at low applied strain the residual strength is higher than is observed when do strain is applied. These results indicate that future work on fluoride glass fibers for use in aqueous environments should focus on optimization of the as-drawn strength of durable glass, such as aluminum fluoride-based material, rather than on making small strength improvements to already strong but less durable glass, since such improvements will be quickly lost in aggressive environments