City of Light: The Story of Fiber Optics

SUBMARINE CABLES 211
1984 they laid 28 kilometers (17 miles) of cable and two repeaters in the
deepest water handy, the eight-kilometer-deep Ogasawara Trench. Careful
tests showed little change, so reassured NTT engineers went ahead with plans
for a submarine cable between Japan’s two main islands. 40
Shark Attack in the Canary Islands
With the lion’s share of the two biggest submarine fiber cables, AT&T was
not about to take chances on an untried technology. The Submarine Systems
division carefully planned another test of TAT-8 technology in the Canary
Islands off Africa, where the Spanish telephone authority wanted a link between
Grand Canary and Tenerife islands. Canary Islanders got the latest
submarine cable technology in return for putting up with exhaustive tests of
the hardware, including trials of recovery of the cable from the ocean floor
and shipboard repairs.
AT&T got more than it bargained for. Installation of the 119-kilometer
(74-mile) cable went well, including a pair of repeaters 40 kilometers (25
miles) apart. Soon afterward, though, engineers noted a short-circuit in the
cable, caused by ocean water, which conducts electricity, reaching the central
conductor that carried electric power for the repeaters. The AT&T team worried
how water was getting into the cable, but it wasn’t an immediate catastrophe
because the cable was designed to withstand a single short. Then a
second short followed, knocking out repeater power and forcing AT&T to haul
the cable up from the ocean floor.
Examining the recovered cable, AT&T engineers found shark teeth embedded
in the outer plastic coating. Sharks had bitten the cable and left some of
their easily detached teeth behind. The engineers were amazed; no one had
ever seen sharks bite undersea coaxial cables, and they had no hint that
sharks might develop a taste for fiber. The marine biologists whom they called
also were amazed. The cable had been more than a kilometer (0.6 mile) deep,
and no one realized that sharks swam that deep.
It wasn’t the sort of thing that normally prompted AT&T press releases,
but word inevitably leaked out. An engineer working on the problem 41 took
a section of cable and a handful of sharks’ teeth to a European conference,
where he showed them to a few insiders. The story was too good for his fellow
engineers to keep quiet. Once an enterprising reporter picked up the lead, it
was all over the papers and the technical press.
Sharks had ignored coaxial cables. Why should they turn their razor-sharp
teeth on fiber? Biologists suggested some experiments. They stretched a cable
across a tank filled with captive sharks and watched the animals. Nothing
happened until they switched on the current that normally powered repeaters,
which prompted some sharks to investigate the cable. The electric field
from the current attracted the predators, who apparently use it in hunting.
Coaxial cable also carried a current, but its outer metal wrap blocked the
electric field from reaching into the water. Nothing blocked the field from