OVERVIEW

The potential of single-crystal fibers was recognized 50 years ago, when the inherent strength and perfection of the crystalline matrix of the fibers were determined. Despite this, sustained research into the production of such fibers was delayed until the 1970s. Until then, control over the growth characteristics of the fibers was poor, and there were no well-defined areas of utilization [1]. The first application that drove the production of single-crystal sapphire fibers was use as a reinforcing member for metal-matrix composites [2]. Sapphire, whose chemical formula is Al ₂O ₃, was thought to be an attractive candidate to employ for this purpose because it possesses a high melting temperature of 2053 C, has a low solubility in water, is resistant to chemically hostile environments, and has many attractive physical and mechanical properties [3]. However, fiberreinforcing applications require fibers to possess good mechanical characteristics, but make no restriction on the optical qualities of the fibers.

Interest in developing optical-quality sapphire fibers emerged after the commercial effort to manufacture structural-grade sapphire fibers began. Sapphire optical fibers are not reasonable candidates for long-distance telecommunications lines because of the difficulties involved in manufacturing low-cost fibers having perfect crystalline structure and surfaces as smooth as conventional silica-based glass fibers. Researchers at Stanford University, realizing that sapphire fibers were not likely to replace glass-based fibers for telecommunications applications, embarked on a program to investigate the potential applications and manufacture of...