City of Light: The Story of Fiber Optics

THREE GENERATIONS IN FIVE YEARS 193
bitter cold froze them at night. Normally, engineers had to adjust the electronics
to compensate for effects of the huge temperature swings on coax.
They didn’t need those adjustments with fiber. 79 It was the sort of thing engineers
noticed. Fiber was ready.
So too, at last, was the ponderous machinery of industrial production.
AT&T and independent suppliers had supplied one-off systems; now they were
making standard hardware using gallium arsenide lasers and graded-index
fibers. They knew better technology was in the works in the labs, but they
thought years would be needed to make it as reliable and economical.
Second-Generation Technology
Even as production lines were starting to roll for first-generation systems, a
second generation was sprouting vigorously from ‘‘hero experiments’’ that
sought to show how far and fast fiber signals could go. In August 1978, NTT
sent 32 million bits per second through a record 53 kilometers of gradedindex
fiber at 1.3 micrometers. 80 In a matter of months, they raised the data
rate to 100 million bits per second. 81 You couldn’t do that at gallium arsenide
wavelengths—Fibers absorbed too much light and pulse spreading limited
transmission speeds.
Steady improvements followed in laboratory system tests. Commercial
companies began to take notice. Corning, determined to fight for the market
by pushing the technology, jumped on the long-wavelength bandwagon with
a dual-window fiber usable at either wavelength. 82 Others offered longwavelength
fibers, and long-wavelength lasers were on the market before Jim
Hsieh had production up and running at Lasertron. Even AT&T worked on
long-wavelength systems, although Bell Labs, wary of laser lifetime problems,
concentrated on 1.3-micrometer LEDs. The LEDs weren’t as powerful as lasers,
but they did not require cooling, and with the lower loss at 1.3 micrometers,
their signals could span ten kilometers (six miles) of graded-index fiber
at the same 45 million bit per second rate as short-wavelength lasers. 83
System developers grew bolder with second-generation systems, partly because
the changes were relatively minor. Long-wavelength graded-index fibers
fit into the same cables and used the same connectors and splices as
first-generation systems. Many transmitters and receivers could be converted
to the long wavelengths simply by plugging in new light sources and detectors;
the new components cost more but paid handsome benefits in longer
repeater spacing.
Rural phone companies were the first to take a serious interest, because
they have to span longer distances than the few miles between urban or
suburban switching offices. Valtec charged boldly into the field, installing a
pair of long-wavelength systems in rural Virginia that ran 18.7 and 23.5
kilometers without repeaters, using its own special graded-index fiber optimized
for 1.3 micrometers. Those were record repeater spacings for any working
system at the start of 1982. Rich Cerny had left to start his own company,