The term glass or a glassy material represents a rather large family of materials with the common characteristic that their structure is noncrystalline. Thus, rigorously speaking, one can produce a glassy material from a polymer, metal, or ceramic. An amorphous structure is fairly common in polymeric materials. It is less so in metals, although metallic glass, generally in the form a ribbon, can be produced by rapid solidification, i.e., by not giving enough time for crystallization to occur. In this chapter we describe silica-based inorganic glasses because of their great commercial importance, as a reinforcement fiber for polymer matrix composites and as optical fiber for communications. Communication via optical glass fibers is a well-established field. All the audio, video, and data transmission that we take for granted today, indeed the whole field of fiber optics, would not be possible without the availability of specialty glass fiber. Charles Kao was awarded the Nobel Prize in physics in 2009 for his work on fiber optics. The Internet as we know it became possible mainly because of undersea cables. The undersea cables for communication became possible because of the optical fiber. As Blum (2012) describes it: light enters the optical fiber at one shore and comes out on the other, which may be as far as two continents away.

Crude optical glass fiber bundles were used to examine the insides of the human body as far back as 1960. Since then tremendous progress has been made in making ultra pure, controlled composition fibers with very low optical signal attenuation. The total worldwide shipment of optical fibers runs into many billions of US$. Before we describe the processing, structure, and properties of glass fiber, it would be appropriate to digress a bit and describe for the uninitiated, albeit very briefly, the basic physics behind the process of communication via optical glass fibers.

In this chapter, we describe the basic physics behind optical communication followed by processing techniques, composition, structure, and properties of glass fibers of different kinds. A new type of glass fiber called photonic bandgap fiber is described. Finally, applications of different types of glass fibers are described.

Basic physics of optical communication

By far the most important and simple phenomenon that is made use of in optical wave guides is refraction of light. Figure 8.1 shows this phenomenon.