City of Light: The Story of Fiber Optics

212 CITY OF LIGHT
reaching the water around the fiber cable, where the sharks could sense it.
Other factors also may have played a role. The Canaries cable hung above
the surface in some areas, and also vibrated, which may have attracted sharks
or simply gotten in their way as they swam.
Engineers took no chances when they returned the cable to the ocean
floor. To deflect sharks’ teeth and block at least part of the electric field, they
wrapped the cable with a strong steel tape. They also extended the armor
normally used to protect the cable in shallow water to depths well below
where the sharks had bitten the cable. As they laid the cable, they made sure
it rested on the bottom rather than hung in the water where it might tempt
hungry sharks. ‘‘We haven’t had a shark bite since,’’ Runge told me with a
grin. 42 The cable remains in regular service.
While shark bites grabbed the headlines, AT&T worried about semiconductor
lasers. Bell Labs had problems making long-wavelength lasers; they
had missed delivery schedules for the Bermuda trials, 43 and reliability was a
continuing concern. Dreading the cost of hauling a repeater from the ocean
floor to replace a dead laser, engineers designed repeaters with three spare
lasers to back up each laser transmitting signals. 44 However, long-wavelength
lasers improved as time passed, and by the time AT&T started building the
final TAT-8 repeaters, they included just one backup laser per fiber. 45 The
transmitters, cable, and receivers also worked better than had been expected
in 1980, allowing AT&T to double repeater spacing from the original plan of
30 kilometers to beyond 65 kilometers. STL and Submarcom were more cautious,
spacing repeaters about 40 kilometers in their parts of TAT-8. 46
Turning the Tables on Satellites
In the mid-1970s, the communications satellite industry thought it might
vanquish costly cables from the transatlantic market. 47 A decade later, fiber
optics had turned the tables. 48 As TAT-8 moved toward completion, international
consortia planned more submarine cables. In May 1986, AT&T, British
Telecom, Teleglobe Canada, and the French and Spanish telephone authorities
agreed to plan and build TAT-9, with service to start in 1991.
The new cable was designed around a fourth generation of fiber technology,
operating at 1.55 micrometers, where fiber loss was lowest. Both Corning
and British Telecom were pushing the advantages of fibers they had developed
with minimum pulse dispersion shifted to 1.55 micrometers. 49 However,
AT&T chose instead to use lasers that emitted an extremely narrow range of
wavelengths, so pulses should suffer little dispersion at 1.55 micrometers.
Their design let them double transmission speed to 560 million bits per second
and stretch repeater spacing to a hundred kilometers in TAT-9. The same
technology later reached 140 kilometers. 50
The satellite industry fought back. The International Telecommunications
Satellite Organization (Intelsat) promised to cut its rates and claimed that new
echo-cancellation circuits made complaints about satellite delays ‘‘spuri-