City of Light: The Story of Fiber Optics

152 CITY OF LIGHT
much that the lasers worked only at liquid-nitrogen temperature. 15 The Russians
were getting discouraged when they looked at some gallium aluminum
arsenide crystals one of them had stashed in a desk drawer a couple of years
earlier. They were delighted to find nothing had happened to the crystals,
showing gallium aluminum arsenide was stable.
Once they realized that, the Russians soon grew heterojunctions using a
technique called liquid-phase epitaxy that Herb Nelson developed in 1963 at
RCA Laboratories. 16 It crystallizes gallium arsenide compounds from a mixture
of molten gallium placed on a semiconductor substrate. This avoids
growth problems arising from differences in melting points of the elements.
Although the Russians made the first heterojunctions, 17 the Iron Curtain and
the need to translate their work into English kept word from reaching America
until a team at IBM had reported the same thing. 18
Heterojunctions revived diode laser development. They were hard to grow,
but they reduced the threshold current needed to drive the laser—and its
rapid increase with temperature. RCA became a hotbed of activity, funded by
military contracts. Henry Kressel and Nelson began making lasers with a
single heterojunction. They gradually perfected the process, reducing threshold
currents so their lasers could fire repeated short, high-power pulses at
room temperature, 19 meeting Army requirements. In April 1969, RCA announced
plans to manufacture single-heterojunction lasers; two months later,
a spin-off—Laser Diode Laboratories Inc.—announced they would, too. 20 The
Pentagon was happy.
The communications industry was not. They wanted semiconductor lasers
that generated a steady beam they could modulate with a signal. The best
hope for that seemed to be a double-heterojunction laser, where a pair of
heterojunctions sandwiched the active layer. Developers hoped that by trapping
electrons better this would improve efficiency and reduce threshold current.
Kressel and Nelson were working on the idea, but military contracts
had taken top priority.
Bell Labs Places Its Bet
Military contracts were not a distraction at Bell Labs, where John K. Galt,
director of solid-state electronics research at Murray Hill, was convinced that
optical communications needed room-temperature diode lasers. In July 1966,
he asked two Bell Labs researchers to figure out why diode lasers had such
high thresholds at room temperature. Chemist Mort Panish, 37, and Japanese
physicist Izuo Hayashi, 45, who had joined the Bell Labs group a month
before, accepted the challenge. Galt didn’t expect them to solve the problem,
but he wanted Bell Labs to learn enough to compete. 21
The two men had complementary skills, although Hayashi’s awkward English
sometimes slowed communication. 22 Panish had studied the chemistry,
physics, and luminescence of gallium arsenide. Hayashi wanted to move into