Optical Fiber Pioneer Shares Physics Nobel

IEEE Life Fellow Charles Kuen Kao came up with the theory behind optical-fiber telecommunications

Photo: Nortel

7 October 2009—The Nobel Prize in Physics was awarded yesterday to IEEE Life Fellow Charles Kuen Kao ”for groundbreaking achievements concerning the transmission of light in fibers for optical communication.”

Kao helped fuel the development of optical fibers, the thin waveguides that route light over thousands of kilometers to deliver telephone, TV, and Internet services. Because optical fibers transmit light, which speeds through wires faster than electricity, they enable high-speed communication and large bandwidth data transfer literally at the speed of light.

Work on optical fibers using long, thin glass wires took shape in the 1950s, as it became apparent that shuttling electrons back and forth wouldn’t support the growing telephone and television industry for long. But because early fibers lost a huge amount of information even over distances as short as a meter, they were useful mostly for endoscopy and other medical applications, not for transmitting information across oceans.

But Kao saw the potential of glass fibers. ”The material is very cheap, as I went to the most abundant material on Earth,” Kao said in a 2004 IEEE oral history. ”And it is also that the fiber itself has very, very good durability. So really it is an ideal thing. It is really the cheapest and strongest material that you can use.”

While working at Standard Telecommunication Laboratories, in Harlow, England, Kao showed that much of the information loss in the optical fibers of the day was due to impurities in the glass threads, not because of any intrinsic property of glass. His 1966 paper with George Hockham demonstrated that an optical fiber could carry the equivalent of 200 TV channels or more than 200 000 telephone channels and predicted that optical fibers would be able to transmit this information while losing only 20 decibels per kilometer, an acceptable loss rate for long-distance communications.

”No one in their right mind thought you could send a signal through glass,” says IEEE historian Robert Colburn, who interviewed Kao in 2004. ”Kao defied the conventional wisdom of the time” by predicting that you could make glass pure enough. ”People said, ’You can’t even see through a foot of glass turned on its side, much less a thousand kilometers long.’ ”

But Kao’s theory persevered, and four years later such fibers were being produced by Corning, in New York state. They were eventually improved to carry multiple wavelengths of light on the same fiber, vastly increasing their communication capacity. Today optical fibers transmit data at astounding rates. Just last week, Bell Labs broke the record for optical transmission, sending the equivalent of 400 DVDs per second over 7000 kilometers, surpassing commercial undersea cables by a factor of 10. Fiber-optic cables are steadily connecting the world, with a 17 000-km cable laid in July linking East Africa to Europe and India, at speeds fast enough to stream high-definition video.

Photo: Richard Epworth

And as the cost of installing fiber-optic cables drops, they are increasingly entering homes. Telecom companies laid about 523 000 km of submarine cable between 1998 and 2002, enabling higher volumes of simultaneous voice calls and data transfer over the Internet. Three million kilometers of optical fiber have been laid in the United Kingdom alone since Kao’s original prediction.

Experimental optical fiber, some of which contains photonic crystals and other unusual structures, promises to pump even more data through the Internet. Photonic crystals, for example, bend light much more sharply than optical fibers can, potentially making the crystals useful for routing light around microchips, which would boost the microchips’ computing capacity.

To Probe Further

Check out an interview with Kao, part of the IEEE History Center’s Oral History Program.

Kao and Hockham’s original paper was published in Proceedings of the IEE in July 1966 and reprinted 20 years later. It’s available here for a limited time. For more cutting-edge technology and seminal research articles, go to IEEE Xplore.

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