City of Light: The Story of Fiber Optics

240 CITY OF LIGHT
innovators were climbing ladders of success in industry and academia. The
revolutionary technology was being accepted into the establishment, where
old timers talked about the glory days.
Yet Keck was right; the revolution wasn’t over. Before things could get
seriously boring, a new generation of revolutionaries emerged from the labs.
They were armed with optical amplifiers and wavelength division multiplexing,
which let them process signals as light instead of as electrons. The second
fiber-optic revolution brought a bandwidth boom that carried fiber into the
spotlight, where the heat of the market created a bubble that—like all bubbles—led
to a bust. Fiber rushed in to quench the Internet’s thirst for bandwidth,
and not even Alec Reeves could have foreseen that fiber could deliver
too much bandwidth.
The Quest for Optical Amplification
The second fiber-optic revolution started quietly in the mid-1980s. Dave
Payne had not set out to start a revolution when he began the work at
Southampton that led to the erbium-doped fiber amplifier. He hadn’t even set
out to invent an optical amplifier. His goal was to develop optical fibers with
unusual properties that let them sense changes in the surrounding environment.
That meant exploring new territory, and scientists know that such
exploration can lead to breakthroughs.
Payne had stayed at Southampton after earning the university’s first doctorate
in fiber optics. Fiber sensing had become hot in the early 1980s. The
U.S. Naval Research Laboratory was developing fiber-optic acoustic sensors
to sit on the sea floor and listen for Soviet submarines. Payne was making
fibers that controlled light polarization, which the Navy needed for its acoustic
sensors. But he kept his eyes open for other ideas, and spotted one from Eli
Snitzer, then at the United Technologies Research Center in Connecticut.
Snitzer had found that a fiber containing a dash of an element called neodymium
could sense temperature by variations in its light transmission. 3
Payne’s specialty was making unusual fibers, and in 1985 his group developed
a new way to add a little neodymium to the core of a single-mode
fiber. The process could be used for a whole family of 14 elements called rare
earths, which included neodymium. Importantly, adding the rare earth had
little effect on fiber loss. 4
Neodymium also made good lasers, so it was natural for Payne to try
making his neodymium-doped fiber into a laser. His group put mirrors on
both ends of a two-meter length, and fired light from a gallium arsenide laser
down the fiber. The neodymium atoms absorbed that wavelength and released
the light energy as a laser beam, as they did in bulk glass. 5 It wasn’t the first
fiber laser, but it was a big advance over earlier ones, so Payne’s group began
playing with it. ‘‘We were making kilometer-long lasers just to see what happened,’’
Payne recalled. 6