City of Light: The Story of Fiber Optics

THE LASER STIMULATES THE EMISSION OF NEW IDEAS 99
Hot air (thin)
Cool air
Hot air (thin)
Figure 8-1: Heating the sides of a hollow tube thins the air along the sides, so its
refractive index is lower than that of the cooler gas in the middle. This refractiveindex
difference makes a gas lens focus light.
the beam wander off the center of the gas lens, and once it slipped off center,
it kept on going. ‘‘The only way to recenter it was by brute force,’’ he recalls,
so he wrote off the gas lens waveguide as ‘‘a dead duck.’’ 37 He predicted long
chains of glass lenses would suffer similar centering problems. An interactive
computer system that sensed beam motion and moved the beam back on
target could solve the beam wander problem, but that seemed a forbidding
task at a time when a computer filled a whole room. Berreman wrote a paper
detailing the problem, but Miller would hear none of it. He sat on the negative
results until one of his own analytical wizards came up with essentially the
same answer. 38
Miller put a new man on gas lenses, Peter Kaiser, who took a new approach.
Kaiser blew cool gas into a hot tube about 6 inches (15 centimeters)
in diameter, so the tube heated gas near the walls to focus light. To bend
light around troublesome curves, he placed vents 30 inches (75 centimeters)
apart. Adding more vents focused light more sharply. He placed about 80 gas
lenses in a demonstration waveguide that ran 200 feet (60 meters) down a
Bell Labs corridor, and found loss was too low to measure. However, the
apparatus was elaborate, and he had to use argon rather than air. 39
Those problems did not discourage Miller and Kompfner, who could see a
role for laser communications in the future that AT&T could carefully plan
as a regulated monopoly. Its Picturephone video-telephone was set to debut
in 1970, and AT&T had planned its evolving network around the new service,
even designating the # key on push-button phones to signal video calls. 40 The
company expected Picturephone to spread steadily but not spectacularly,
reaching 100,000 sets in 1975 and a million in 1980. Millimeter waveguides
would provide the extra long-distance capacity to handle the early years of
that growth, but AT&T expected to need the tremendous capacity of optical
waveguides would be needed once Picturephones became commonplace,
probably after 1990.
Bell expected either gas or glass lens waveguides to be so elaborate and
expensive that they would have to carry at least a million telephone circuits
to be economical. 41 That was not a showstopper for the world’s biggest and
richest telephone company. Thanks to regulations that assured the company
a return on its investment, AT&T had ample money to spend on both approaches,
as well as on other research even less likely to generate near-term