City of Light: The Story of Fiber Optics

GUIDING LIGHT AND LUMINOUS FOUNTAINS 15
recalled that Jacques Babinet, a French specialist in optics elected to the academy
in 1840, had made similar demonstations in Paris. Babinet focused candlelight
onto the bottom of a glass bottle as he poured a thin stream of water
from the top. Total internal reflection guided the light along the jet, illuminating
a china plate or sheet of paper at the end. Arago asked Babinet to
write up his work.
Well established as a lecturer and instrument maker, 9 Babinet complied,
but he wasn’t as eager for recognition as Colladon. His brief account suggests
he didn’t think the whole thing was very important, and Colladon probably
put on a better show. Yet, in passing Babinet mentioned something else. The
idea also ‘‘works very well with a glass shaft curved in whatever manner,
and I had indicated [it could be used] to illuminate the inside of the mouth.’’ 10
Colladon mentioned only water jets; Babinet, who specialized in optics,
extended the principle to guiding light along bent glass rods. Since glass fibers
are merely very thin glass rods, that meant he anticipated the idea of fiber
optics. He even suggested a practical application that would resurface a half
century later: dental illuminators. Yet Babinet also knew the limits of glass
technology. Examining lighthouse lenses, he had found that the best glasses
of his time were not very clear, so light couldn’t go far through them. Look
into the edge of a sheet of plate glass today, and you can see the same green
color Babinet saw a century and a half ago. It’s no wonder he thought light
guiding little more than a parlor trick.
The Magic of Glass
Babinet probably also doubted light guiding in glass was new. It almost certainly
was not. Glass dates back at least 4500 years to ancient Egypt and
Mesopotamia. 11 By 3500 years ago, Egyptians were sculpting miniature heads
of transparent glass, which the years have since turned milky white. 12
Ancient and medieval glass workers must have seen glass rods guide light.
For 2000 years, glass blowers have thrust glass tubes into glowing furnaces
to soften them. Workers pausing to relax from the hot, hard job must have
seen the fiery glow of the furnace emerging from the glass. Master glass
makers noted total internal reflection as they made sparkling ornaments for
the bright glass chandeliers that illuminated the great rooms of the rich. But
they kept their secrets to themselves. Scientists began to study total internal
reflection in medieval times as they sought to understand the mystery of the
rainbow, 13 but they did not understand it until the laws of refraction were
formulated in the seventeenth century.
By the mid-nineteenth century the cutting edge in physics had moved
elsewhere. The industrial revolution made glass commonplace in windows
and bottles. Babinet may have felt his brief report in Comptes Rendus only
restated the obvious. After sending his letter to Arago, Babinet apparently
never returned to the guiding of light before he died in 1872.