City of Light: The Story of Fiber Optics

204 CITY OF LIGHT
between them, and that was bad news. Repeaters are expensive and their
electronic innards are the parts of a submarine cable most likely to fail (excluding
cable breaks). The more repeaters, the higher the cost and the more
likely trouble. AT&T designed a new coaxial cable to carry 16,000 voice
circuits, but it would have required twice as many repeaters as TAT-6—one
every 4.6 kilometers (2.9 miles), or a thousand to cross the Atlantic. 9
You also need thicker cables to carry higher frequencies, and their bulk
posed another problem. 10 The TAT-6 cable was 2.08 inches (5.28 centimeters)
thick, and engineers worried that a fatter cable would not fit on a single
cable ship, increasing installation costs. They also worried that bulky, inflexible
cables could be damaged more easily during installation or handling.
As coax looked worse and worse, satellites were looking better and better.
However, cable operators couldn’t simply switch to satellites; they had been
frozen out of the satellite business in the 1960s. Nor was it easy for cable
manufacturers to turn to making satellites. Moreover, while satellites benefited
from the allure of space-age technology, they also suffered some technical
limitations that affected how they relayed telephone signals.
One is transmission delay. Standard communication satellites circle the
Earth exactly once a day, so they appear to park above a spot on the equator,
where they remain continually in range of ground stations. 11 This requires
them to orbit 22,000 miles (36,000 kilometers) above the surface. Radio
signals travel at the speed of light, but at that distance radio waves take a
quarter-second to make the round trip. The number sounds vanishingly small,
but it’s enough to throw off your verbal timing in a call with one satellite
bounce. A second satellite bounce adds further delay, making conversation
difficult.
Poor connections were a problem with the analog electronics used by satellites
through the 1980s. Some circuits suffered annoying echoes; a few carried
screeching feedback. Sometimes only one side of the conversation went
through. If you made many international calls in the 1980s, you learned to
recognize satellite circuits and were ready to hang up and try again if you
needed a better circuit.
Satellite channels also lacked security. In the heyday of the Cold War,
Soviet and American security agencies tried to eavesdrop on each other’s
satellite links. They didn’t always get the information they wanted, but the
threat made military agencies prefer cable links.
Unwilling to abandon transoceanic communications, AT&T, the British
Post Office, and Nippon Telegraph and Telephone sought alternatives to coaxial
cables for undersea transmission. With hollow millimeter waveguides
out of the question under four miles of water, optical fibers were virtually the
only possibility. Engineers did not have to start from scratch. They could adapt
existing submarine cable structures to accommodate fibers instead of coaxial
cables. Electro-optic repeaters could fit into the same pressure-resistant housings
as coaxial repeaters. As fiber-optic communications evolved, the main
issue became assessing different approaches.