City of Light: The Story of Fiber Optics

100 CITY OF LIGHT
profits. Nor were research managers deterred by technical difficulties; millimeter
waveguides had come a long way in the past dozen years. ‘‘Today there
are probably more physicists and engineers working on the problem of adapting
the laser for use in communication than in any other single project in
the field of laser applications,’’ Miller wrote in the January 1966 Scientific
American. 42
Checking Long Shots
Bell Labs also searched for long-shot alternatives to confocal or gas-lens optical
waveguides. One idea was making hollow waveguides from nonconductive
dielectrics or reflective metals. The numbers looked good for 0.25millimeter
tubes if they were perfectly straight—a third of the light would be
lost in a kilometer-long metal tube, and just a little more would be lost in a
dielectric. However, bending caused serious problems. Loss of a metal guide
doubled if it was curved over 48 meters (157 feet), comparable to a freeway
off-ramp. The dielectric guide was much worse, with loss doubling for a 6mile
(10-kilometer) bend. 43 Those numbers, and the difficulty of making thin,
perfect tubes, stopped that line of research.
Optical fiber was hard to ignore. Kapany’s Scientific American cover story
on fiber optics appeared as Javan closed in on the helium-neon laser. Bell had
its own resident fiber expert, Jeofry Courtney-Pratt; he didn’t work in communications,
but when he saw a 1961 paper 44 that described a fiber as a
waveguide, he passed it along to Miller. 45 Miller was intrigued by the idea of
optical analogs of solid plastic microwave waveguides.
However, the reality was daunting. Kompfner cut to the heart of the issue
by asking a simple question: How clear are the best glasses? Calls to glass
manufacturers and trips to the reference library yielded similarly discouraging
answers. The clearest glasses had attenuation of at least one decibel per meter.
That meant that 20 percent of the light entering a fiber was lost going the
width of a desk. That was adequate for an endoscope, which need only reach
into the stomach. It was hopeless for communications. Go 4 meters (13 feet),
the width of a typical room, and you lose 60 percent of the light. Go a hundred
meters—the length of a football field—and only one ten-billionth (10 �10 )
of the light remains. It was no wonder Kompfner said ‘‘forget it.’’ 46
The door at Bell Labs stayed closed for years. When Kompfner outlined
optical communications research in 1965, he shrugged off optical fibers because
‘‘numerous serious problems’’ remained unsolved. 47 In mid-1966, Miller
and Roy Tillotson reviewed optical communications for the technical journal
Applied Optics, but said nary a word about fibers. 48
They saw the millimeter waveguide as the next generation of communications
technology. By 1966, Bell Labs had buried several miles of experimental
millimeter waveguide at Holmdel and was designing solid-state repeaters.
A single two-inch waveguide was designed to transmit 50 channels