City of Light: The Story of Fiber Optics

126 CITY OF LIGHT
it made eminent sense. Like glass, sugar melts to a thick liquid that can be
drawn into fibers (cotton candy), but sugar melts at 107�C (225�F), so it can
be handled in brass crucibles instead of the high-temperature materials
needed for glass. Dyott dyed the inner core red and started drawing sugar
fibers. By adjusting composition to control the refractive index of sugar, he
could draw single-mode sugar fibers. The fibers were totally unsuitable for
telecommunications, but they helped Dyott understand the physics of making
fiber.
Roberts knew nothing about the experiments until January 1969, when
he asked Dyott about fiber-drawing progress as they shared a train compartment
riding to Sheffield. ‘‘I mentioned that we were using sugar, and he blew
his top,’’ says Dyott. The precise manager considered the experiments ridiculous;
to him, the only proper way to examine a process was by writing and
solving formal mathematical equations that gave exact numerical results.
Furious that Dyott could not be bothered to do the requisite calculations,
Roberts transferred fiber drawing to Daglish. He dutifully set to work with
pencil and paper, telling Dyott, ‘‘If Sir wants it calculated, Sir will have it
calculated.’’ However, the calculations were beyond Daglish as well, and work
stalled until an exasperated Roberts transferred Daglish completely out of fiber
optics. George Newns inherited the double-crucible project, and he eventually
resorted to experiments with a core of molasses and a cladding of sugar syrup.
The two liquids did not solidify, but they yielded enough information to design
a platinum double-crucible system for drawing glass fibers, and Newns got
away with it. 46
Newns ordered the purest available raw materials and started drawing
fibers at Dollis Hill, but industrial northwest London was a poor environment
to use ultrapure materials. He was one of the first people that the Post Office
moved to its newly built research laboratories in Martlesham Heath, near
Ipswich, some 100 kilometers (60 miles) northeast of London. There he found
that platinum particles from the crucibles contaminated the glass, so he
switched to crucibles of fused silica, which remains hard at temperatures
much higher than the 1000 to 1200�C (1800 to 2100�F) melting temperatures
of the compound glasses he was using. 47
Bell Labs Wakes Up
Kao’s careful measurements of fused silica forced Bell Labs to take fibers more
seriously. At Murray Hill, the center of Bell’s materials research, Dave Pearson
put his low-level study of optical fibers on the front burner, adding several
people, 48 including two from Miller’s group at Crawford Hill.
Like the British Post Office team, Pearson’s group saw little hope for fused
silica and concentrated on multicomponent glasses. They had no glassmaking
facilities, so they had outside contractors make glass from the purest
available raw materials. They measured light transmission in bulk glass and
in fibers. They tested fibers made from rod-in-tube preforms, and assembled