City of Light: The Story of Fiber Optics

206 CITY OF LIGHT
1978, when they became the first developers to commit to using single-mode
fiber for any real system. 13 They had ten years to go before the scheduled
laying of the first big submarine fiber system, TAT-8 across the Atlantic.
Serious Single-Mode Development
Bell Labs cautiously waited a few months before pulling the plug on development
of coaxial submarine cables. Some engineers doubted a fiber system
would be ready by the TAT-8 target date, but fiber was the last chance for
submarine cables. Coax had no prayer of keeping up with satellites.
Bell added fiber experts to the submarine cable group in Holmdel, which
began working with Bill French and Paul Lazay, who were drawing singlemode
fiber at Murray Hill. Peter Runge shifted from Stew Miller’s group to
take charge of developing submarine fiber cables. The task promised Runge
personal as well as professional rewards; the transplanted German engineer
had family on the other side of the Atlantic, familiar voices that passed beneath
the sea.
Adapting the tried and true designs of submarine cables for fibers was a
top priority. Cables are built outward from their centers. The starting point
for the submarine fiber cable was a copper-clad steel ‘‘king wire,’’ to provide
essential strength. A soft plastic cushion covered it, with up to a dozen optical
fibers embedded in it, gently wound round and round the king wire in a helix.
Nylon covered the plastic, forming a core 2.6 millimeters (0.1 inch) thick.
Then heavy steel strands were wound around the core, strengthening and
shielding the fiber-optic heart of the cable. A welded copper tube covered the
steel wires; its role was to carry electric current to repeaters across the ocean.
A thick layer of solid white polyethylene covered the copper, making a 21millimeter
(0.827-inch) cable ready to lay on the sea floor like a thick, fat
garden hose. The cablers wound extra heavy steel wires around lengths of
cable to be laid in shallow water, where fishing trawlers might drag their
lines across it. Tests of 100-meter (330-foot) samples began in September
1979, 14 in an artificial ocean Bell Labs had built at Holmdel to test the coaxial
cables for TAT-6. Elaborate instruments controlled temperature, pressure, and
cable tension. 15 The results looked good.
Standard Telephones and Cables took undersea cables even more seriously.
They were an important part of the company’s business, and by 1978 the
submarine systems division was responsible for fiber manufacturing and the
main supporter of fiber development at STL. 16 A major STL worry was that
the high pressure at the bottom of the ocean would cause the fiber to wrinkle
inside the cable, causing ‘‘microbends’’ that let light leak out. To assess the
problem, they designed a cable with four graded-index and two single-mode
fibers inside an inner aluminum tube, which was surrounded by steel strength
wires, a concentric copper conductor, and an outer polyethylene layer, with
18 armored protective layers wound around the outside. They assembled 9.5
kilometers (5.9 miles) of cable, which the Post Office carefully laid in Loch