The 2009 Nobel Prize in physics has been awarded to three researchers whose work has formed the basis of modern telecommunications and digital imaging. The prize recognizes Charles K. Kao, whose discoveries led to a breakthrough in fiber optics, and Willard S. Boyle and George E. Smith, who invented the CCD (charge-coupled device) image sensor.
Optical fibers carry almost all telecom data and form the backbone of the Internet. “When combined with the laser and the transistor, the invention of an efficient, low-loss optical fiber has made nearly instantaneous communication possible across the entire globe,” H. Frederick Dylla, director of the American Institute of Physics, said in a statement.
The work was done in the mid-1960s. The invention of the laser in the early 1960s spurred researchers to develop a practical transmission medium for light, which can transmit data much faster than radio waves. Optical fibers, however, didn’t seem promising at the time because of their high rates of attenuation: only about 1 percent of the light sent through the fiber would be transmitted as far as 20 meters.
Kao’s insight was to focus not only on the physics of light, but on the material properties of the medium itself. In 1966, as a young engineer at Standard Telecommunication Laboratories in Harlow, U.K., Kao discovered the underlying causes of attenuation in optical fiber: iron impurities were causing it to absorb and scatter the light. Pure glass, he suggested, would make a better carrier and would also present cost advantages.
After further studies of how light of different wavelengths travels through different media, Kao and his colleagues pointed to silicon dioxide as the best material. But silicon dioxide is difficult to work with. A team of researchers at Corning Glass Works realized Kao’s designs in 1970, using a high-pressure reaction chamber to form the first low-loss optical fibers, and others at Bell Laboratories refined the manufacturing technique to bring down the cost.
Modern optical fibers are even better than what Kao predicted, losing just 5 percent of the light over a distance of a kilometer. In 1988 the first intercontinental optical fiber, which was 6,000 kilometers, was laid down between Europe and America; today there are over one billion kilometers of optical fiber around the world, with more being added each day.
The other half of this year’s Nobel Prize in physics goes to the inventors of the CCD, a device that converts images into electrical signals, thereby revolutionizing photography and digital imaging.
While Kao’s work grew out of a concerted effort to find a better telecommunications medium, Boyle and Smith’s was unanticipated. They developed the CCD at Bell Labs in 1969, after having sketched out the basic design during an hour-long brainstorming session. The principle behind the CCD is the photoelectric effect, which was in part theorized by Albert Einstein, earning him the Nobel Prize in 1921. When bombarded by a photon, some materials emit an electron. Boyle and Smith’s design is a silicon chip whose surface is covered with a grid of capacitors that store the electrons created when the chip is illuminated. Each capacitor is a pixel. The number of electrons stored at each capacitor is proportional to the intensity of the light in that part of the image. The image can be read out by pulling the charges off the CCD.
The advantage of the CCD over light-sensitive chemical films and even the human eye is its high sensitivity. Over the entire spectrum of light, from infrared to x-rays, CCDs can capture 90 percent of incoming photons. The eye or a film camera captures only 1 percent of these photons.
A year after their invention, Boyle and Smith made a video camera based on the digital-image sensor; in 1981 Sony brought to market the first CCD camera, the Mavica. Astronomers were early adopters and have used the sensors to capture images of distant celestial objects that were heretofore invisible.
Today the CCD faces some competition from another digital-imaging chip invented around the same time–CMOS (complementary metal-oxide-semiconductor). Both devices rely on the photoelectric effect. While the CCD directs electrons off the chip in a single stream to be read out, data from CMOS pixels are read out on site, which saves power and prolongs battery life. However, CMOS is not as sensitive as CCD, which still has advantages for advanced applications like astronomy and medical imaging.
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