City of Light: The Story of Fiber Optics

108 CITY OF LIGHT
date the fiber guide appears to hold most promise if due to advances in materials
technology it becomes possible to manufacture cladded fibers having
effective loss ...about two orders of magnitude better than at present.’’ 14
In France, Spitz asked the French glass manufacturer Saint Gobain to make
glass cylinders with thin inner cores, which could be drawn down into fibers.
Then he assigned further research to Alain Werts, who had just started at
CSF after finishing his undergraduate degree. 15 Spitz and Simon also studied
ways to suspend thin unclad fibers in air. 16 That would not improve light
collection, but it would make the filaments easier to handle.
A Search for New Waveguides
While Toni Karbowiak knew ultraclear glass could cure the problems of clad
fiber waveguides, he was not a materials specialist and had no idea how to
make it. He did know waveguide theory, and he applied that expertise to
inventing a new type that could guide light along its surface with low loss.
A crucial problem was suspending it without obstructing the surface wave.
He devised a simple and elegant alternative to hard-to-handle fine filaments:
a flat waveguide a fraction of a wavelength thick but many wavelengths wide.
His theoretical analysis showed the thin film ribbon could guide light along the
middle of its surface in a single mode, although not in the same mode as a cylindrical
fiber. It could be a centimeter or more wide, large enough to collect light
from a focused laser beam. Because light traveled along the middle, a frame supporting
the edges would not affect the surface wave. He predicted its loss should
be no more than a few decibels per kilometer—so roughly half the signal that
entered the waveguide would remain after one kilometer.
Nothing confined the light in the plane of the thin film, but twisting the
waveguide in a spiral pattern should avoid ‘‘any noticeable loss of energy,’’
Karbowiak wrote after filing a patent application in April 1964. 17 He hoped
to reach attenuation of a few decibels per kilometer at infrared wavelengths
of 1 to 10 micrometers. 18 After finishing his theoretical work, Karbowiak
asked Kao and Hockham to make and test samples. It became their top priority.
Number two on the list was finding low-loss materials to clad fiber
waveguides. That looked like a long shot, because Toni Karbowiak, like Rudy
Kompfner, had already ascertained that the clearest optical glass on the market
was far too lossy for the job.
An Unexpected Offer
As Kao and Hockham struggled with the tough problems of making thin-film
optical waveguides in late 1964, opportunity knocked unexpectedly for Karbowiak.
With a doctorate and some three dozen articles published in scholarly
journals after a decade at STL, he was a technical heavyweight at 41. The
University of New South Wales thought he would make an ideal chair for its