City of Light: The Story of Fiber Optics
City of Light: The Story of Fiber Optics
City of Light: The Story of Fiber Optics
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Seeking a Better Magic Ingredient<br />
BREAKTHROUGH 145<br />
As others tried to identify the mystery ingredient in Corning’s first low-loss<br />
fiber, Schultz sought better dopants. Corning reduced loss <strong>of</strong> titania-doped<br />
fibers to about 10 decibels per kilometer, but they remained extremely fragile.<br />
Schultz wanted something that increased the refractive index <strong>of</strong> fused silica,<br />
without absorbing light or requiring the troublesome heat treatment. He also<br />
wanted a material that made a better glass.<br />
<strong>The</strong> chemistry <strong>of</strong> glass is tricky, in an entirely different league from things<br />
that fizzle in high-school test tubes. Glasses are unusual solids that form only<br />
when certain liquids are cooled in the proper way. As most liquids freeze,<br />
atoms link up in ordered crystalline lattices. In a glass, the atoms retain the<br />
random arrangement <strong>of</strong> a liquid, but are frozen in place. 44 Only a few materials<br />
form glasses; silica is among the best. Titanium dioxide, a compound<br />
called ‘‘titania,’’ is not a glass-former. Silica can form a glass if it contains a<br />
dash <strong>of</strong> titania, but mix in too much titania, cool the liquid too slowly, or do<br />
any <strong>of</strong> a thousand other little things wrong, and the solid crystallizes instead.<br />
Germanium was a logical alternative. Just a row below silicon on the<br />
periodic table, it has similar chemistry and is also a glass-former. It absorbed<br />
little light and did not require the troublesome heat treatment. Schultz also<br />
found problems: Germanium oxide (or ‘‘germania’’) evaporated more easily<br />
than silica, which complicated glass formation. Nonetheless, in early 1972<br />
Schultz adjusted the flame-hydrolysis process and started doping preform<br />
cores with germanium instead <strong>of</strong> titanium.<br />
By then, Corning was scaling up fiber development, adding people and<br />
investing money, but still cautious because the future was far from assured.<br />
<strong>The</strong> changes meant Keck, Schultz, Maurer, and Zimar no longer had to do<br />
everything themselves. Technicians and other scientists helped them mount<br />
the germanium-doped preforms in the furnace and draw fiber from them.<br />
Keck took samples to his lab and measured them. Even the first <strong>of</strong> the<br />
germanium-doped fibers looked encouraging.<br />
It wasn’t long before Keck had results good enough to invite Maurer’s boss<br />
to take a look one Monday morning. However, when he set up the test, not<br />
a speck <strong>of</strong> light went through the fiber. Keck sputtered an apology and set to<br />
work finding the problem. He discovered the problem arose from Corning’s<br />
habit <strong>of</strong> shutting down air conditioning over the weekend. Humidity built up<br />
and the cardboard reel holding the fiber expanded, stressing the fiber such<br />
that it wrinkled, forming tiny ‘‘microbends’’ where light leaked out. Microbend<br />
loss had shut down light transmission totally. Keck rewound the fiber<br />
and called the man back down to show that he’d solved the problem. 45 With<br />
a little experimentation, he and Schultz reduced loss to a mere four decibels<br />
per kilometer. It was June, 1972, not quite two years after they had broken<br />
the 20 decibel per kilometer barrier.<br />
‘‘This was to my mind the breakthrough for fiber optics, because it was<br />
now a practical fiber,’’ says Schultz. ‘‘It didn’t break, you didn’t have to go<br />
through all this other stuff. You could make fibers right <strong>of</strong>f the draw with