City of Light: The Story of Fiber Optics

246 CITY OF LIGHT
the same type of fiber along the whole system. If they used two types with
different values of dispersion, the different dispersions could cancel each other
out. If one fiber let the short wavelengths fall behind, they could balance that
by adding a second fiber that let the short wavelengths go faster. At any point
along the fiber, the dispersion was high enough to prevent crosstalk. But the
sum total of dispersion in all the fiber segments would be low.
Corning developed a special fiber that allowed the slow wavelengths to
catch up with the fast ones, canceling out the dispersion of other fibers, which
solved the problem. 30 By 1995, NTT was able to send 10 billion bits per
second at each of 16 separate wavelengths through 1000 kilometers of fiber
using dispersion compensation and erbium amplifiers. 31 Solitons, which had
gotten off to an early lead, were now falling behind. Dispersion control was
simpler and easier, and it was ready when the need came for more bandwidth.
Internet Bandwidth
Bandwidth in communications always seemed like closet space in a house—
you could never have enough. Through the 1990s, experience confirmed that
analogy. Long-distance companies had tried to build ample bandwidth during
the first fiber-optic boom of the 1980s, often including extra fibers for future
growth. But by the mid 1990s those fiber cables were filling up. Fibers had
brought down the cost and increased the demand for long-distance calls. Fax
machines were humming with traffic that would have gone by mail or express
carrier a few years earlier, further increasing demand. But the real growth
was in computer data.
The spread of personal computers in the 1980s created a demand for data
connections. They began with 300-baud modems linking computers to each
other through the phone network. Commercial digital communication services
followed, with modem speeds increasing. The Internet followed. It began
as a network linking computers at a number of government and academic
research centers. It grew as new users adapted it for electronic mail. It took
off with the spread of the World Wide Web. Launched in 1991 by a group
at the European Center for Nuclear Research (CERN) in Switzerland, the web
had only 500 servers at the start of 1994. By the end of the year 10,000
servers were connected. 32 That drew more users, and business smelled money
and followed.
Low-bandwidth modem connections were fine for text-only e-mail. The
graphics-intensive Web needed much more bandwidth. Corporate data transmission
requirements also were growing. Data traffic exploded. For a brief,
heady interval in 1995 and 1996, Internet traffic doubled every three to four
months, as hordes of new users discovered the net. That was a factor of 10
or more a year, an incredible growth rate by any standard. Internet traffic
was but a small fraction of the volume of ordinary telephone traffic. Yet
telephone traffic was growing a mere 10% a year. It seemed only a matter of
time before the Internet would dwarf the venerable telephone industry.