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