6.1 INTRODUCTION

The last two decades of the twentieth century saw an immense increase in the number of applications in which optical fibers of different kinds were used. The explosive development of fiber optics for communication was a major driving factor behind this progress, providing the necessary tools and enabling technologies. Contrary to popular belief, however, the development of the optical fiber was not initially driven by the needs of the communications sector but has a much longer history. For instance, the controlled guiding of light in a transparent water jet was first described in 1841 [1]. The technology subsequently found use for the spectacular illumination of water fountains at the great exhibitions of the late nineteenth century. A short notice in The Lancet [2] issue of 1889 described the use of a glass light guide for purposes of medical examination, and the 1920s and 1930s saw the development of the concept of fiber bundles for image transfer in medical and other applications. These were the driving forces behind such important inventions as, for example, the glass clad fiber, which gained commercial success in medical endoscopes as well as faceplates for image intensifier devices in the early 1960s. Up to this time, optical fibers had been of the multimode type. The single-mode optical fiber was discovered and described about the same time [3]. With the invention of the laser and the techniques for making low-loss fibers...