strand that is a single fiber-optic cable

It all seemed magical, and it was about to get even better. That sleek preform goes into a draw tower—imagine a grain silo on stilts up near the ceiling of a giant warehouse—to be melted.

Then from the gob of stuff that initially protrudes from the bottom of the tower following the melting process, a single strand is pulled or drawn straight down toward the ground. That is the hair-thin strand that is a single fiber-optic cable.
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The melting and drawing process, like the other steps, is tightly controlled. First, the tip of the preform is heated, causing a gob of hot glass to descend. Once the gob drops, it’s taken away, and the thin thread behind it is threaded through a device that minutely controls the speed of the draw (the speed at which the strand is drawn toward the ground) and the diameter of the resulting fiber. Every micron is documented.

The glass cools rapidly, within seconds, but according to precise timing. Meanwhile, inside the draw tower, a coating made of several layers of different plastics is applied to protect the glass and cured using ultraviolet light.