City of Light: The Story of Fiber Optics

142 CITY OF LIGHT
The few other fiber papers at the meeting surprised Maurer. Thinking he
was in a tight race, he hadn’t turned around to study the field behind him.
After he crossed the finish line, he was amazed to see everyone else remained
far, far behind.
Barlow opened a general discussion at the end of the meeting by asking
what technology would come next, the metal waveguide or the optical fiber.
One Post Office engineer said the millimeter waveguide was the obvious
choice because it was ready for installation. Heady with bravado after hearing
Maurer’s report, Dyott brashly retorted, ‘‘I’m quite happy for you to lay the
waveguides, and we will come along later and fill them with optical fibers.’’ 34
Guarding Snips of Fiber
The Post Office invitation was too good an opportunity for Maurer to resist.
It came from a driving force in the field and a major potential customer. Dollis
Hill had developed equipment to measure fiber properties, which in the early
days was a tricky task, and independent confirmation of Corning’s results
would be an important plus.
The basic concept of measuring loss in an optical fiber is simple: Compare
how much light enters the fiber with how much emerges from the far end.
Divide to get the fraction of light emerging, take the logarithm, multiply by
ten, and you get fiber loss in decibels. Light output was easy to measure, but
not how much light entered the fiber. Especially in the early days, most light
aimed at the fiber would not wind up in the tiny core. Early fiber developers
found the best way to account for light that missed the fiber core was to work
backward. They first measured how much light emerged from the end of a
long piece of fiber. Then they cut the fiber close to the light source, leaving
only a segment too short to have much loss of its own. The amount of light
exiting the short fiber should be essentially what entered the other end. Dividing
the output of the long fiber by that of the short fiber gave the loss.
The cut-back method yields good results, but it consumes fiber. Every new
measurement requires chopping another segment from one end of the fiber,
so you have to have enough fiber to spare. You can’t repeat measurements.
More worrisome for Corning, which wanted to keep its fiber composition secret,
it breaks off little pieces of fiber, which someone might analyze to determine
its content. It was bad enough that Corning’s fibers were very brittle;
cut-back measurements could sprinkle fiber segments around the lab for
anyone to pick up.
Nonetheless, the Post Office measurements were crucial to establish Corning’s
credibility. Corning carefully wound a long length of precious brittle
glass thread on a paint can, then packed it in a custom-built container that
looked like a hat box and bought a seat for it on the plane. Maurer sat beside
the box, and he or Chuck Lucy, who went with him to discuss business
prospects for fiber, kept a hand on it at all times. 35 It was an odd-looking