* Deep inside Cheyenne Mountain at Colorado Springs, the computers of the North American Air Defense Command are wired with whisker-thin glass fibers. Bundled together in finger-sized cables, the strands carry reams of defense data as well as up to 3,000 phone calls at once between the mountain bunker and nearby Peterson Air Force Base.

* In Biarritz, France, residents will soon see some of the long-touted dreams of the "information age" come true: videophones, Yellow Pages telephone listings that pop up on TV screens, living-room access to "libraries." A key ingredient: hundreds of miles of glass fibers.

* At the sprawling United Technologies research facility in East Hartford, Conn., technicians peer inside jet engines using nail-sized probes made from thousands of fused glass fibers. The probes allow them to watch combustion and spot hairline cracks inside the engines -- where temperatures top 2,500 degrees F.

Around the world, light-bearing strands of glass finer than fishline are helping to recast the way people see and communicate.

Called fiber optics, the technology permits images and messages to be sent through light pulses beamed down superpure glass threads -- and could be the brightest glimmer on the high technology horizon since the microchip.

Although the technology has been around since the 1950s, it is now starting to roll out of the laboratory and revamp everything from defense work to dental tools.

Perhaps the biggest boom, however, is occuring in the telecommunications field, where optical fibers are replacing bulkier and less efficient copper wire systems.

Indeed, a finger-sized fiber-optic cable can carry 40,000 phone calls at once , in contrast to only 20,000 with two wrist-sized copper cables. Scientists speculate fiber cables may one day bear upward of a million simultaneous conversations.

Messages are sent along a strand of glass with a system that works like a swarm of lightning bugs trained in Morse code. In conventional telephone systems, for example, the voice is translated into bursts of electricity, which flow down a copper wire or coaxial cable. In an optic fiber system, the conversations are turned into light pulses by lasers the size of a pinhead. Television images can be sent the same way. In fact, last year's Winter Olympics at Lake Placid, N.Y., were broadcast with the help of fiber-optic wiring. Cable TV will be a major market for fiber optics.

Each time the laser is switched on or off, one "bit" of information is moved. Systems now being developed will be able to send 274 million bits per second -- enough to transmit the entire contents of a 24-volume encyclopedia in six minutes -- at double the rate at which the best copper-wire systems could do it.

he conduit for all of these super-quick light pulses is made of glass more than 1,000 times clearer than ordinary window glass. If the ocean were filled with the same material, you could see to the bottom at any depth.

Fuse these crystalline strands together and they become a kind of optical transmitter, channeling an image from one end of the bundle to the other. With such optical probes, scientists can peer into jet engines or down one's throat.

The project in Biarritz, France, is one of the more ambitious "glasswiring" schemes on the drawing boards. It will help bring videophones, multichannel TV, and other services to 1,500 dwellings by mid-1983. Some 5,000 subscribers are eventually slated for hookups.

Backed by government funds, phone companies in France, as well as those in Canada, Britain, and West Germany are busy adapting fiber-optic technology to their needs. British Telecom, an arm of its Post Office, is devising an undersea cable to link up with the United States.

The Japanese, too, are pushing fiber-optics technology, particularly in some developing countries where the new systems don't have to be grafted onto existing wire networks.

Many industry observers, in fact, suggest the US is falling far behind Japan and Europe in the high-stakes race for a share of the world market.

These countries have "the equivalent of a NASA program going on, while we are standing still," says Herb Elion of International Communications & Energy, a consulting firm in Framingham, Mass. "Even if we made a major effort, we would be five years behind."

In an indirect way, the story of fiber-optics development goes back as far as the ancient Phoenicians. These Mideast dwellers fused different-colored pieces of glass together to make jewelry. Although used only for decoration, the ornaments transmitted images much the same way fiber bundles do today.

It was eons, however, before glass was spun into threads. This happened as early as 1887 in Britain, when a venturesome tinkerer named C. V. Boyes shot molten glass out of a crossbow, producing fibers 100 to 200 feet long. He didn't see much use for them though, except possibly as Torsion springs.

A little earlier, in 1880, Alexander Graham Bell had developed a photophone that bounced light beams off a mirror.

Fiber optics as it is known today was spawned in the 1950s, when engineers began to use the strands to carry images. The early glass bundles were used as medical probes and as inspection tools for rifle bores. At one time there was talk of using them to peer into the subterranean life of groundhogs and moles.

Yet the practical means for harnessing light to transmit voices remained a mirage. It finally came about with two developments: the introduction of lasers in the early 1960s, and, in 1970, the development by Corning Glass works in New York of a material pure enough to transmit light without significant "leakage."

Today's fiber cables are usually sheathed in plastic and metal. They can be as strong as steel, yet the fibers themselves are pliable enough to be tied in knots.

Their purity makes window glass look like a chalkboard. "The clarity is outside the expression of most people . . . ," says David Charlton, Corning's supervisor of marketing and advertising. "It is like looking through a vacuum."

Several frontiers are being explored to put the new technology to work. One potential use is fiber-optic sensors, tools that would use light pulses to detect minuscule changes in temperature or movement. Such light sensors in effect would enable the computer to simulate the human sense of touch.

At United Technologies (UT) in East Hartford, for instance, scientists working in cinder-block cubicles are developing sensors that will measure the movement of an airplane rudder down to 1/4000th of an inch. Light pulses are beamed down a set of fibers, and the signals then bounce back to indicate its position.

In one pastel-colored room, Dr. William Morey picks up a heater that resembles a hair dryer and aims it at a fiber bent in the shape of a teardrop. A small metal box begins to flash numerals in red. What's happening? The heat affects the flow of light through the filament, and the temperature change is recorded in Lilliputian amounts.

Similar sensors may one day be mounted on planes, or even in cars and trucks, to gauge engine temperatures and thus help improve fuel efficiency. Other sensors are being developed to measure stress on metal; they could be used to test strains on aircraft wings, among other things.

"We're really at the most rudimentary stages of the technology and how to use it," says Dr. Elias Snitzer, a pioneer in the field and manager of applied physics at the UT research center.

Overall, fiber optics will make the "information age" economical, industry observers predict. It will bring the so-called office of the future down to the pocketbook of the average person.

How is America using the technology already?

In the telecommunications field, Bell Telephone installed its first experimental "light loop" in Atlanta five years ago. Since then, the company has laid short stretches of glass cable in Chicago, San Francisco, Orlando, Phoenix, and Sacramento, among other areas. Glass trunk lines will link Pittsburg with Greenburg, Pa., and White Plains, N.Y., and Manhattan by year's end.

Other loops are slated for traffic-congested areas such as San Francisco, Los Angeles, and Greenville, Texas. All told, Bell officials will lay more than 14, 000 miles of glass fiber this year, which will amount to a few hundred miles of cable since each cable contains up to 144 fibers. By 1984, a 611-mile line is expected to link Washington and Cambridge, Mass. It will be able to carry 80, 000 conversations simultaneously. Telephone officials plan eventually to put down a 3,500-mile transatlantic cable.

Besides boosting carrying capacity, fiber optic cuts down on transmission loss. Present cables use "repeaters" to amplify the message every mile or two. With a fiber optic system, messages can be beamed four to five times that distance before fading.

Yet the world isn't likely to be wrapped in a cocoon of glass fiber overnight. Despite bullish predictions, it remains far too costly to string the fibers into individual homes on a wide scale. Nor is the average home equipped with the photophones and other space-age hardware that demands the carrying capacity of optical fibers.

So most lines in the US are being installed between main telephone exchanges in traffic-congested areas. Messages are sent out electronically, beamed down glass trunk lines in the form of light pulses, and then switched back to electrical pulses before reaching home phones.

Industry officials, however, expect mass production of the fiber systems to reduce costs. And, they note, the cost of copper wire is bound to go up as world supplies dwindle, while glass cables, whose basic building block is sand, will drop in price.

In the defense area, glass wires are showing up in Navy ships, military transport planes, and Army field communications systems. Commercial airlines are eyeing glass wiring.

The fibers are immune to electrical interference from such sources as lightning strikes, and they eliminate the problem of bothersome crosstalk. Since light doesn't permit electronic "eavesdropping," the fibers could be useful for communication in high-security areas, as well.Another plus: no risk of an electrical fire.

At computer-clogged offices, glass fibers will link data-flush information centers. And the fibers are also expected to play a big role in bringing cable television into homes.

Or consider another possibility: You're driving down the road, and your auto starts to cough. You pull over, peer into the engine with a fiber-optic periscope, and tinker with the timing. Farfetched? Maybe. But keep your wrench handy. Cars may one day be equipped with optical fibers, which, when plugged into a dashboard computer, will help "sense" engine problems.

Other current uses include long, snaky fibers that peer into out-of-the-way pipes; probes perched on the tip of arc welders that allow the operators to watch dangerous work from a distance; "face plates," made up of millions of fused fibers, that enhance night vision. (The latter are cropping up in light-amplifying rifle sights, telescopes, and goggles that look like stubby binoculars.)

"What fiber optics provides is one more optical tool for people to use in extending their imagination to solve problems," American Optical's Dr. Walter Siegmund sums up.

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