City of Light: The Story of Fiber Optics

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