City of Light: The Story of Fiber Optics

164 CITY OF LIGHT
A pair of wires carried 24 digitized voice channels, combined into a single
stream of 1.544 million bits per second, with a repeater every 6000 feet (1.8
kilometers) to boost signal strength. By 1970, a whole hierarchy of faster
digital systems were on the drawing boards. Each step up involved combining
or multiplexing slower signals, to be separated at the other end. The digital
pipes interfaced with digital switches, special-purpose digital computers hardwired
to route telephone signals to their proper destinations. The second step
in the hierarchy, called T2, merged four T1 lines on wires, a total of 6.3
million bits per second. Combining seven T2s gave a T3 carrier at 45 million
bits per second, a speed Bell had not decided how to transmit. Six T3s combined
to make a T4 signal, 270 million bits per second or 4032 voice circuits,
routed over coaxial cables or microwaves. 23 Millimeter waveguides were to
be the next step, with each pipeline carrying sixty T4 signals, 240,000 voice
circuits or about 17 billion bits per second. 24
Those plans assumed that video communications would follow speech as
surely as television had followed radio. Bell Labs had sought that goal since
the 1920s, when it competed with C. Francis Jenkins to devise mechanical
television transmitters. 25 Top AT&T management had planned the Picturephone
revolution to start in 1970, with service in Manhattan and Pittsburgh.
The whole Bell System was designed to handle the new technology once you
pushed the # button on your Touch-Tone phone to signal a video call. 26 Each
Picturephone circuit needed the equivalent of a hundred voice lines, so the
network would need plenty of new capacity, assuring a place for millimeter
waveguides.
That well-planned future started to unravel before regular Picturephone
service began. New York state regulators blocked the new service in Manhattan
until the phone company improved its regular service. AT&T inaugurated
Picturephone service June 30, 1970, with only 38 sets at eight companies
in Pittsburgh, but that did not deter the optimists. The front page of
the New York Times proclaimed, ‘‘A major stride in the development of communications
was taken today.’’ 27 AT&T predicted 100,000 Picturephones
would be in use by 1975.
Potential customers didn’t agree. A year later, only 33 Picturephones were
operating in Pittsburgh, and only 12 could call beyond their buildings. ‘‘The
thing hasn’t really grown the way we thought it would,’’ admitted a phonecompany
marketer, although higher officials maintained that its time would
come. The Times—perhaps a bit embarrassed itself—buried its follow-up story
on page 26. 28
Still sure that the time would come for the millimeter waveguide, Bell
planned a full-scale field trial in 1974, the first outside the lab. 29 To avoid
troublesome mode problems, the waveguides were buried in trenches as
straight as arrows. The tubes were filled with pure dry nitrogen, because
oxygen in the air absorbs millimeter waves. Nobody pretended it was going
to be cheap or easy, but with government regulations assuring a return on
its investment, AT&T was ready to spend untold billions.