Communications are increasingly based on electro-optic systems in which telephones, television and computers are linked by fiber optic cables which carry information by light.
Making glass optical fibers is a highly specialised aspect of glass manufacture. Optical fibers consist of two distinct glasses, core of highly refracting glass surrounded by a sheath of glass with lower refractive index between the two glasses, it is guided by total internal reflection at the coresheath interface to the other end of the fiber. In theory, a wide range of glasses can be used as long as the difference in refractive index is appropriate but the higher the refractive index of the core relative to that of the sheath glass, the greater the carrying capacity of the fiber. A typical system available commercially comprises a germanium doped silica core and a borosilicate cladding.
The aim in manufacture is to produce a fiber of glass which is so pure and free from defects that light inserted at one end will emerge at the other end a distance of 1 kilometre or more away. There are many manufacturing processes being used to produce cored fiber; two of these will illustrate the principles. All the processes require ultra-pure starting materials.
