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Optical fiber is a single, hair fine filament drawn from molten silca glass. Today, this has replaced metal wires in high speed communication.In a fiber optic communications system, cables made of optical fibers connect datalinks that contain lasers and light detectors. To transmit information, a datalink converts an analog electronic signal into digital pulses of laser light. These travel through the optical fiber to another datalink, where a light detector reconverts them into an electronic signal. It makes people to wonder how something only 1/8 of a mm - 0.005 inches - in diameter can be made with such precison. So here is breif explanation of how optical fiber is made.
Raw Materials
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Optical fiber is mostly made from silicon dioxide(SiO 2 ) but some little amount of other materials such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire, are used for longer-wavelength infrared or other specialized applications.Chemical compounds such as germanium tetrachloride (GeCl4 ) and phosphorus oxychloride (POCl3 ) can be used to produce core fibers and outer shells, or claddings, with function-specific optical properties.
why silca? 
Silica, which be drawn into fibers at reasonably high temperatures, has a fairly broad glass transformation range. One other advantage is that fusion splicing and cleaving of silica fibers is relatively effective. Silica fiber also has high mechanical strength against both pulling and even bending, provided that the fiber is not too thick and that the surfaces have been well prepared during processing. Even simple cleaving (breaking) of the ends of the fiber can provide nicely flat surfaces with acceptable optical quality. Silica is also relatively chemically inert. In particular, it is not hygroscopic (does not absorb water) also it can be doped with various materials. Silica fiber also exhibits a high threshold for optical damage. But, pure silca is not best suitable for optical fiber, because it exhibits a low solubility for rare earth ions. This can lead to quenching effects due to clustering of dopant ions. These properties makes silca most widely use material for optical fibers.
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