City of Light: The Story of Fiber Optics

116 CITY OF LIGHT
Table 9-1 What Decibel Losses Mean in Optical Fibers and Elsewhere
Loss in
decibels
Fraction of power
remaining Physical analog
0.2 0.954992586 Loss undetectable by the eye
0.5 0.891250938 Light lost reflecting from aluminum
1 0.794328235
10 0.1 Reflection from a dark surface
20 0.01 One percent of light remains
30 0.001 One part per thousand
40 0.0001
50 0.00001
60 0.000001 One part per million
100 10 �10 One part in 10 billion
200 10 �20
300 10 �30 One atom in a ton of matter
400 10 �40
500 10 �50
600 10 �60 Less than one atom in the sun
700 10 �70
800 10 �80 One atom in the visible universe
900 10 �90
1000 10 �100
Werts and Spitz measured some glass losses and borrowed other material
data from Kao. 41 They also borrowed Hockham’s data on the effects of waveguide
irregularities. Werts had to stretch the fibers they got from Saint Gobain
to shrink the cores so they carried just one mode. ‘‘The only originality of
my work,’’ he recalls, was showing that fiber properties could limit light transmission
to a single mode. 42 (Snitzer and others had observed modes in bundled
fibers but had not systematically studied individual fibers.)
No one considered the fiber project particularly important. Werts took a
while to get around to writing the paper, and when he did both Simon and
Spitz declined to be listed as co-authors. It appeared in the French-language
journal L’Onde Electronique 43 just two months after the Kao and Hockham
paper was published in England. There the matter stopped. The military
money was gone, and no one at CSF was willing to bet his reputation on
fiber-optic communications. ‘‘I didn’t really consider at that time it was an
important paper,’’ recalls Spitz. He had ample reasons to be skeptical. French
glass specialists told him that it was impossible to remove the iron impurities
Kao considered the main cause of glass absorption. Other projects looked more
promising; his group turned to storing data in optical form, an idea that led
to today’s audio compact discs and computer CD-ROMs. 44