City of Light: The Story of Fiber Optics

REFLECTIONS ON THE CITY OF LIGHT 235
in 100,000. Each precision laser costs $60,000. To measure the power at
each wavelength used in the experiments you need several optical spectrum
analyzers, boxes that run about $50,000 each.
Generating 20 billion pulses a second is a stretch. The fastest test sets
produce only 10 billion per second and cost $400,000. It takes a separate
$100,000 box to double the speed to 20 billion bits. That’s half a million
dollars, so separate instruments for each channel would blow even Bell Labs’
budget. The Crawford Hill team instead runs all the channels through the
same test set, then splits them apart and adjusts them to make each signal
seem independent.
More costly and delicate instruments are scattered about the lab. A highspeed
oscilloscope to examine the shapes of the pulses runs $50,000. Optical
amplifiers are $20,000. Another rack has six shelves, each holding reels with
120 kilometers of fiber; three more racks bring the total to 3000 kilometers
in the lab. My eyes scanned the boxes and my mind ran a quick total: $2
million worth of instruments in a room about 20 feet (6 meters) square. The
staggering bill means that fewer and fewer groups can run system experiments.
It may be good for Bell Labs, said Chraplyvy, ‘‘but it’s bad for scientists,
because progress comes from a lot of people racing each other.’’ 21
Seven months later, Bell Labs reached the trillion-bit milestone. Chraplyvy’s
group scraped together eight more lasers to make a total of 25. They
split each laser output into beams with two different polarizations, and modulated
each of the 50 signals at 20 billion bits per second. Then they sent it
through 55 kilometers of fiber and reported the results at the annual hero
experiments session at the Optical Fiber Communications conference. 22 By
then, the split of Lucent Technologies from AT&T had divided the group between
AT&T Research and Bell Labs, although all still worked at the Crawford
Hill building.
However, the high cost of the experiments had not kept the Japanese out
of the race. In fact, Fujitsu Laboratories won it, by combining the signals from
55 lasers modulated at 20 billion bits per second. That yielded 1.1 trillion
bits per second, and Fujitsu sent the signals through 150 kilometers of fiber—
nearly three times as much as Bell Labs. 23 It was an impressive, headlineearning
demonstration.
Nippon Telegraph and Telephone Laboratories was not to be left out. At
the same conference, they reported sending a trillion bits per second through
40 kilometers of fiber using a different technique. They generated ten wavelengths
from a single light source, and modulated each one at 100 billion
bits per second. 24
To fans of the fiber-optic performance Olympics, those are elegant and aweinspiring
demonstrations. A dozen years earlier, people dismissed Will Hicks
as a wild-eyed dreamer for suggesting such speeds might be possible. Today
they require extraordinary effort, and some techniques used to set records
may never prove practical. Yet others point the way to future developments,
and commerical versions of the equipment may be only a few years away.