Whatever the future holds, the laser's status as a world-changing innovation has already been secured by its role in long-distance communications. But that didn't happen without some pioneering on another frontier—fiber optics. At the time lasers emerged, the ability of flexible strands of glass to act as a conduit for light was a familiar phenomenon, useful for remote viewing and a few other purposes. Such fibers were considered unsuitable for communications, however, because any data encoded in the light were quickly blurred by chaotic internal reflections as the waves traveled along the channel. Then in 1961 two American researchers, Will Hicks and Elias Snitzer, directed laser beams through a glass fiber made so thin—just a few microns—that the light waves would follow a single path rather than ricocheting from side to side and garbling a signal in the process. Whatever the future holds, the laser's status as a world-changing innovation has already been secured by its role in long-distance communications. But that didn't happen without some pioneering on another frontier—fiber optics. At the time lasers emerged, the ability of flexible strands of glass to act as a conduit for light was a familiar phenomenon, useful for remote viewing and a few other purposes. Such fibers were considered unsuitable for communications, however, because any data encoded in the light were quickly blurred by chaotic internal reflections as the waves traveled along the channel. Then in 1961 two American researchers, Will Hicks and Elias Snitzer, directed laser beams through a glass fiber made so thin—just a few microns—that the light waves would follow a single path rather than ricocheting from side to side and garbling a signal in the process. This was a major advance, but practical communication with light was blocked by a more basic difficulty. As far as anyone knew, conventional glass simply couldn't be made transparent enough to carry light far. Typically, light traveling along a fiber lost about 99 percent of its energy by the time it had gone just 30 feet. Fortunately for the future of fiber optics, a young Shanghai-born electrical engineer named Charles Kao was convinced that glass could do much better. Working at Standard Telecommunications Laboratories in England, Kao collected and analyzed samples from glassmakers and concluded that the energy loss was mainly due to impurities such as water and minerals, not the basic glass ingredient of silica itself. A paper he published with colleague George Hockham in 1966 predicted that optical fibers could be made pure enough to carry signals for miles. The challenges of manufacturing such stuff were formidable, but in 1970 a team at Corning Glass Works succeeded in creating a fiber hundreds of yards long that performed just as Kao and Hockham had foreseen. Continuing work at Corning and AT&T Bell Labs developed the manufacturing processes necessary to produce miles of high quality fiber.
At about the same time, researchers were working hard on developing a light source to partner with optical fibers. Their efforts were focused on semiconductor lasers, sand-grain-sized mites that could be coupled to the end of a thread of glass. Semiconducting materials are solid compounds that conduct electricity imperfectly. When a tiny sandwich of differing materials is electrically energized, laser action takes place in the junction region, and the polished ends of the materials act as mirrors to confine the light photons while they multiply prolifically. At about the same time, researchers were working hard on developing a light source to partner with optical fibers. Their efforts were focused on semiconductor lasers, sand-grain-sized mites that could be coupled to the end of a thread of glass. Semiconducting materials are solid compounds that conduct electricity imperfectly. When a tiny sandwich of differing materials is electrically energized, laser action takes place in the junction region, and the polished ends of the materials act as mirrors to confine the light photons while they multiply prolifically. Three traits were essential in a semiconductor laser tailored to telecommunications. It would have to generate a continuous beam rather than pulses. It would need to function at room temperature and operate for hundreds of thousands of hours without failure. Finally, the laser's output would have to be in the infrared range, optimal for transmission down a fiber of silica glass. In 1967 Morton Panish and Izuo Hayashi of Bell Labs spelled out the basic requirements in materials and design. Two other Bell Labs researchers, J. R. Arthur and A. Y. Cho, subsequently found a way to create an ultrathin layer of material at the center of the semiconductor sandwich that produced laser light with unprecedented efficiency.
By the mid-1970s all the necessary ingredients for fiber-optic communications were ready, and operational trials got under way. The first commercial service was launched in Chicago in 1977, with 1.5 miles of underground fiber connecting two switching stations of the Illinois Bell Telephone Company. Improvements in both lasers and fibers would keep coming after that, further widening light's already huge advantage over other methods of communication. By the mid-1970s all the necessary ingredients for fiber-optic communications were ready, and operational trials got under way. The first commercial service was launched in Chicago in 1977, with 1.5 miles of underground fiber connecting two switching stations of the Illinois Bell Telephone Company. Improvements in both lasers and fibers would keep coming after that, further widening light's already huge advantage over other methods of communication. Any transmission medium's capacity to carry information is directly related to frequency—the number of wave cycles per second, or hertz. The higher the frequency, the more wave cycles per second, and the more information can be packed into the transmission stream. Light used for fiber-optic communications has a frequency millions of times higher than radio transmissions and 100 billion times higher than electric waves traveling along copper telephone wires. But that's just the beginning. Researchers have learned how to send multiple light streams along a fiber simultaneously, each carrying a huge cargo of information on a separate wavelength. In theory, more than a thousand distinct streams can ride along a single glass thread at the same time.
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