City of Light: The Story of Fiber Optics

128 CITY OF LIGHT
Japanese companies started working intently on graded-index fibers. Attenuation
remained a problem, but Nippon Sheet Glass claimed loss as low
as 100 decibels per kilometer by the end of 1969. 53 They couldn’t do that
well consistently; their typical value was 200 decibels per kilometer. Nonetheless,
it was progress.
Building Real Systems
Standard Telecommunication Labs worked hard on demonstrations as well
as on improving fibers. Kao asked Chown, a radio engineer, to build a demonstration
system. Chown decided to build a digital repeater, a device to detect
a weak optical signal, convert the light into electrical form, and amplify the
electronic signal to drive a laser transmitter. Repeaters are vital for long systems,
and they demonstrate the essential components of a communication
system—a transmitter and receiver. Chown designed his to operate at 75
million bits per second. 54
Light detectors and electronic amplifiers were easy to build. The laser
source was a much tougher problem. Everyone wanted to use semiconductor
lasers, but they had to be kept chilled in liquid nitrogen lest they burn out.
Chown had to build a miniature transmission line to deliver short but powerful
electrical pulses to a cooled laser chip the size of a grain of salt packaged
in a metal case about the size of a pencil eraser. To collect the light, he drilled
a hole in the window in the case through which the light normally emerged,
stuck the fiber through, and glued it to the laser. 55
Chown proudly demonstrated the repeater at a 1969 exhibition run by
the Physical Society. Alec Reeves was not impressed; his mind had once more
drifted to the future. He thought it awkward to convert an optical signal into
electronic form, then back into light again. Reeves wanted a purely optical
amplifier, which could amplify a light signal without first converting it into
electronic form. 56 However, Kao was delighted, considering the demonstration
as a sign that fiber communication was ‘‘ready to be moved into the development
phase.’’ At the very least, it convinced ‘‘industrial leaders, responsible
government officials, and technocrats alike ...torecommend further investment.’’
57
Investment was on Kao’s mind because his growing fiber-optic program
kept running over budget. When the time came for his annual budgetary
pilgrimage to ITT headquarters in New York, Sandbank suggested a severalfold
increase in what had been a nominal budget for fiber research. Although
he could report progress, he hesitated to ask for too much money.
When his turn came at the meeting, he outlined his plans for trying to make
low-loss fibers. Al Cookson, corporate vice president of engineering, asked
what would happen if the initial approach did not work.
Sandbank said he would try another one.
The American asked, ‘‘in series or in parallel’’—electronic jargon for one
at a time or all at once.