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On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 30 May, 2007 Next Week's Question
Fiber optics has roots in 19th century fountain displays
Question
How long ago were fiber optics developed?

Question
Optical fiber had its roots in the artful displays of water jets of 19th century fountains. In the 1840's, physicists Jacques Babinet and Daniel Collodon showed that light could be guided inside fountain streams by a phenomenon later named total internal reflection. Total internal reflection is the fundamental principle that allows modern fiber optic cable to guide light signals over transoceanic distances. When a light ray travels from a material for which the speed of light is slower into a material where it is faster (from higher index of refraction to lower index), there is a range of angles for which all of the light reflects back. Since the index refraction of water is greater than air, Babinet and Collodon were able to use total internal reflection to bounce light off the water-air interface and prevent it from escaping into the air. Similarly, modern fiber optic cable is constructed from two kinds of glass so that light totally internally reflects off the interface between a high-index core where the light resides and the lower-index surrounding glass known as the cladding.

The first demonstration of what we would call fiber optics was for medical imaging. Because fiber optics are so flexible, they can be used to transmit images from hard-to-reach places. In 1957, physician Basil Hirschowitz snaked the first fiber endoscope (device for imaging inside the human body) made from a bundle of glass-clad fibers down his throat to view the inside of his own stomach. Today fiber endoscopes are used for a number of non-invasive medical procedures, such as colonoscopies.

It was recognized soon after that fiber optics could be useful for transmitting information encoded on light signals to increase the speed of communication systems. However, the fibers used by Hirschowitz were too "lossy" for practical use in communications. In 1970, a research team at Corning Inc. in nearby Corning, NY discovered the correct glass materials and fabrication process that has made fiber optic communications possible. Prior to fiber networks used today, telephone and media companies transmitted information exclusively on electrical signals via radio waves or over copper wire. If you try to transmit a 10 gigabit per second signal (10 billion bits of information per second) over the best electrical cable you will get half the signal out over just six feet. The other half is lost to heat in the copper molecules similar to how your microwave gives up heat to water molecules in food. In fact, the faster you drive the electrical signal the more power you lose. On the other hand, if you encode the same signal onto a beam of light and transmit it through fiber optic cable, you will get half out after nine miles!

Unlike copper cable, with fiber optics you can increase the signal's speed up to the frequency of the light itself (about 100 trillion bits per second, though we're not quite there yet) with no additional penalty in loss. This capacity for transmitting ultrafast signals over long distances is the main reason why telephone and cable television companies have switched to fiber optic delivery. The reason you plug an electrical cable into the back of your TV at home instead of an optical fiber is because the cable company converts the optical signal back to electrical at the neighborhood level. This may change in the near-future as telecom companies are hoping to deploy a fiber to every individual home to increase the amount of information delivery even further.

For more information on the history of fiber optics see the book City of Light by Jeff Hecht. Additional information on the advantages of fiber optic technology can be found on Corning Inc.'s website at: http://www.corning.com/opticalfiber/library/tutorials.aspx.