Acid stripping of fused silica optical fibers without strength degradation

Abstract

Glass optical fibers are almost always coated with a polymer immediately after drawing to protect them from subsequent handling damage. When studying the strength and fatigue properties of the fibers, it is useful to be able to remove this coating in order to directly observe the fatigue properties of the glass in immediate contact with the environment. Fused silica optical fibers are frequently stripped by immersion in hot (∼200°C) concentrated sulfuric acid. Two recent papers have claimed that hot acid stripping significantly degrades the strength and increases the width of the strength distribution. However, there is a large literature that implies that, at least for most coating systems, acid stripping does not degrade the strength provided sufficient care is taken to protect the bare fiber surface during stripping and subsequent testing. This paper explicitly proves this result, showing that careful complete stripping has little or no effect on the strength of fiber tested in both tension and bending. It is also shown that the immersion time in the hot acid has no noticeable effect on the strength. Experimental protocols are described that minimize the likelihood of accidental damage to the fiber during stripping.