The birth of fiberoptics from "light guiding".

Abstract

VISUAL EXAMINATION OF AND INTERVENTION IN the urinary crannies, crevices, and cavities constitute the cornerstones of endourology. In this endeavor, adequate light transfer for proper visibility has been a perennial hurdle. From the early attempts at reflecting sunlight onto head mirrors to the use of candles and oil wick lamps to incandescent light bulbs, it has been an uphill journey until the advent of rod lenses and fiberoptic light transmission. Thanks to the fiberoptic principles, we now have near-natural quality and quantity of illumination for our endoscopic examinations. Yet this monumental invention began as a mere eye-catching gimmick or parlor trick more than 160 years ago.1 It was 1841. Daniel Colladon, a young professor of physics at the University of Geneva, was to demonstrate fluid flow through various holes of a cistern as part of his lecture on fluid dynamics. However, the lighting in the 19th Century lecture hall was inadequate for such demonstration. Colladon decided to illuminate his display by focusing sunlight with a lens onto the water tank. To his surprise, and the amusement of the assembled, the light spectacularly illuminated the water jets squirting out through the holes of the tank. The light rays trapped in the fluid by total internal reflection traveled along the curving arc of the water until the jets broke up in sparkles of light. It was thus demonstrated that light, which was believed to travel only in a straight line, could be made to follow a curve. The show was impressive, “one of the most beautiful and most curious experiments that one can perform in a course on optics,” wrote Colladon, who coined the term “light guiding” for the physical phenomenon.2 Enamored of and amused by the display, Colladon popularized his show as part of his lecturing repertoire to the intelligentia. The light source was modified into an electric arc light instead of the sun by his contemporary August de la Rive. To establish his claim as the originator of “light guiding,” Colladon submitted a report to Comptes Rendu, the official journal of the French Academy of Sciences. Francois Arago, the editor of the journal, recalled a recent demonstration of a similar phenomenon by Jacque Babinet in Paris and invited him also to write a report. Colladon and Babinet’s separate papers were published in the same issue of Comptes Rendu.2,3 Colladon happened to be a more eager promoter than Babinet, who was already an established academician and not so hungry for publicity. Babinet specialized in optics and extended the phenomenon of guiding light along bent glass rods. He mentioned in passing that the idea works well with glass shafts curved in whatever manner and could be used to illuminate the inside of the mouth, thereby hinting at what would evolve as fiberoptics.3 Although Babinet did not pursue light guiding experiments any further, Colladon’s interest showed sporadic sparks of practical application of his trick. In 1853, he used light guiding as