City of Light: The Story of Fiber Optics

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Fibers of Glass
I do not believe, if any experimentalist had been promised
by a good fairy that he might have anything he desired,
that he would have ventured to ask for any one thing with
so many valuable properties as these fibers possess.
—Charles Vernon Boys, 1889 1
T he difference between glass rods and glass fibers is merely a matter of
diameter. Anyone who can be trusted with a chemistry set can draw a
fiber easily from a glass rod. Hold the two ends of a rod several inches long
and put the middle in a hot flame. The heat softens the glass, melting the
rigid solid into a thick, viscous liquid. After the rod becomes flexible, pull the
two ends apart while removing the rod from the flame. The molten glass
stretches into a long, tapered thread, which solidifies almost instantly as air
cools it. Although the material remains glass, the thin filament is flexible and
seems much less brittle than the rod.
Glass is an unusual material; few others form thick liquids easy to stretch
into fibers. Most liquids are like water, far too thin to make fibers from. Only
if you load water with sugar and heat the mixture do you get a hot, thick
syrup that can be spun into threads of cotton candy.
It is the malleability of hot glass, as well as the transparency of the solid,
that have made it a material for the ages. The ancients probably made the
first glass by accident, when they mixed sand, soda, lime, and ash in a fire
and discovered their creation when the embers cooled. Ancient glass makers
learned how to mold and blow hot glass, shaping it into works of art and
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