19.1 INTRODUCTION

It is widely recognized that the need for larger bandwidths for communication systems was the main driving force for the development of optical fibers. The invention of the laser in 1960 triggered great expectations regarding the possibility of increasing the amount of information carried by a modulated wave using an optical signal. Simultaneously, it was acknowledged that a suitable transmission medium was needed so that optical signals could propagate over long distances with minimum losses. Today several technological barriers have been broken, leading to the development of optical communication systems relying on optical fibers as a transmission medium. Such systems not only have fulfilled the needs foreseen in the early 1960s but also have enabled the development of more sophisticated technologies. Optical communication systems can now manage simultaneously the transmission of video, data, and voice, thereby conveniently exploiting the large bandwidths offered by optical fibers.

Throughout the years, fabrication methods for low-loss silica fibers have improved considerably, and it is now possible to tailor the spectral properties of glass fibers when using the appropriate materials within the core. However, in the early stages, liquids were among the first materials tested as core media for optical fibers. While solid materials fully compatible with silica had not been found, several liquids offered two main features that were attractive enough for fiber fabrication: a low-absorption coefficient and a refractive index higher than that of glass. Thus,...