Lasers are everywhere

From...

May 31, 2000
Web posted at: 10:22 a.m. EDT (1422 GMT)

by Mathew Schwartz

(IDG) -- They're the basic parts of your CD player, the supermarket checkout scanner and the writing head of your laser printer. But when most people think of lasers, it's in terms of the frontiers of medicine -- if not as the weapon of choice for extraterrestrial evil geniuses. One legacy of lasers' prominence in science-fiction books and movies is their power as symbols of futuristic technology, even as they've become the backbone of the telecommunications industry today.

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Now Novalux Inc., a Sunnyvale, Calif.-based start-up, has invented a new laser, called the Novalux Extended Cavity Surface Emitting Laser (NECSEL). The NECSEL greatly increases the amount of information that can be inexpensively sent over fiber. That's music to the ears of an industry growing at 40% per year. Soon, lasers could even let you communicate wirelessly, or they could substitute for the picture tube in your television.

"The simplistic concept (of lasers) probably derived from that old James Bond movie of a laser driving down at Sean Connery. It was a big-old device with a circular beam coming down. Conceptually, that's kind of correct, but all lasers today with those big beams come from gas or material lasers," says Malcolm Thompson, president and CEO of Novalux and former chief technology officer at Xerox Corp.'s Palo Alto Research Center. More common today are minute semiconductor lasers, such as those found in the printer heads of laser printers.

How Laser Works

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When the U.S. Academy of Sciences its list of the top 20 scientific accomplishments of the 20th century, lasers and fiber optics were on it, alongside electrification. But when the laser was invented, it wasn't to solve a pressing social or scientific problem.

"A number of my friends used to kid me about it -- 'Nice solution, but what can it do?' They didn't see much in it," says Charles Townes, a scientific adviser to Novalux. He is honored as co-inventor of the maser -- which is similar to a laser but uses microwaves rather than light -- and the laser. Townes received the first patent for lasers as telecommunications devices in 1960. In 1964, he was awarded the Nobel Prize in Physics.

Townes, then on the faculty at Columbia University in New York, had set out to invent a better method for measuring light waves.

"I'd never heard of a detached retina, but that was one of the first medical applications for lasers," he says.

Lasers are more commonly used to tune fiber-optic transmissions, generate and amplify signals and distribute those signals via fiber optics. To understand what constitutes a laser telecommunications breakthrough, it helps to understand how lasers work.

Laser stands for "light amplification by stimulated emission of radiation." Simply put, when you stimulate the electrons in an atom, they jump to a higher-energy orbit. But because this orbit is unstable, the atoms fall back into their normal orbits, emitting photons -- light waves -- as they do so. This is the principle behind anything that emits light.

Identical atoms will have identical jumps in energy states when stimulated and also travel in parallel. If you can make multiple atoms release light energy simultaneously, then those light waves will stimulate one another, increasing in power until they potentially produce a large, coherent beam. On the other hand, if a wave contacts an unexcited atom -- as often happens -- the wave dissipates.

In the early history of lasers, finding the appropriate material to stimulate atoms to the point where they would "lase" -- produce laser light -- was the Holy Grail. Theodore Maiman solved that problem by using a synthetic ruby to build the first working laser. Both sides of the ruby were reflective, though one only partially. Maiman pumped blue light into the ruby, which interacted with chromium impurities, thus exciting the atoms and producing laser light.

Maiman's was a solid-state laser -- the solid being a ruby -- but there are various media that lase: solids, gases, liquids and semiconductors. Each produces beams of various frequencies and strengths, all suited to different applications. Large lasers that cut materials -- such as the one used against James Bond in Goldfinger -- are typically gas lasers.

A Better Beam

On the other hand, semiconductor lasers, which are much more common, are very small and use very little power. There are two kinds: edge-emitting and vertical-cavity. In edge-emitting lasers, which are less expensive than vertical-cavity lasers, the sides of the semiconductor are cleaved to make a mirror, and the beam shoots out of the edge. While more than 50 million are manufactured every year and used in devices such as CD players, the mirrors and thus the beam are imprecise and aren't suited to high-speed networking.

Fiber optics relies upon the more precise vertical-cavity lasers. These are created on small wafers by the thousands; the lasers themselves can be smaller than 1mm3. Manufacturers create very precise beams by building more than 100 layers into each mirror -- known as the upper and lower Bragg mirrors -- on the laser.

Precision also begets efficiency: Whereas an edge-emitting laser in a CD player requires about 30 milliwatts to function, a vertical-cavity equivalent would require only 2 milliwatts. The rounder the beam, the more precisely the laser "couples" with the fiber-optic cable, sending signals farther down the cable before they need to be strengthened, which saves money. More powerful lasers also increase transmission efficiency.

Novalux has invented a more powerful, 300-milliwatt vertical-cavity laser that is smaller than similar lasers and less expensive to manufacture. "The things that limit the continued extensibility of the fiber-optic network are cost and performance of future lasers. Lower cost could drive much more fiber into metropolitan areas," says Thompson. Fiber-optic cable is cheap; lasers aren't. Thompson predicts his company will eventually be able to create a very small 1-watt NECSEL as well.

Fast Forward

Expect to see the NECSEL hit the market early next year, assuming it completes mandatory testing conducted by Telcordia Technologies Inc. (formerly Bellcore). Morristown, N.J.-based Telcordia certifies that third-party equipment meets networking standards. In the meantime, new uses for lasers are continually being invented. The following are several examples:

• Wireless data transmission: Lasers can be used for so-called free-space data transmission -- such as that offered by start-up TeraBeam Networks in Seattle, which uses lasers for wireless, line-of-sight networking. It could be especially cost-effective in metropolitan areas. One advantage is that the medium -- air -- is unregulated and therefore cheap. A disadvantage is that poor weather can compromise beam quality. TeraBeam expects to introduce products to service most major U.S. markets within three years.
• Fiber to the curb and home: The barrier to ubiquitous high-speed household and business access is the so-called last mile. Because of the expense of laying fiber-optic cable and the lasers needed to send signals, most telecommunications companies use copper to cross the last mile. However, copper wires can't carry more than 10M byte/sec. Lines can be used in tandem to improve that performance, but then the cost increases. Once the price of lasers decreases and they can be installed in every home cost-effectively, fiber optics and greater bandwidth for the home will be viable.
• Automotive: "You can expect to see fiber in every car," says Gary Oppedahl, vice president of operations at Novalux. "Why do you need something that fast in a car? Weight." Automakers are adding more and more systems to their cars but are constantly trying to lighten vehicles. Mercedes-Benz is already using fiber to keep weight down. Just as copper wiring in cars was replaced by silicon, so, too, will fiber, a plastic, further decrease the loads of today's cars.
• Digital theater: "If you've got a beautiful, circular, well-behaved beam, you can project it infinitely and begin talking about electronic cinema," says Thompson. Since lasers provide almost molecular-level control of an image, very controlled front- or rear-projection displays ranging from desktop to cinema size or greater are very possible, at exceptionally high quality. In the near future, TV tubes and flat-panel displays could become obsolete.
• Lidar: Light detection and ranging (lidar) is similar to radar. But where radar uses radio waves to measure speed, distance and direction, lidar relies upon a laser diode. It also uses a much narrower beam, producing better readings. Unlike conventional radar, laser light is potentially much harder to detect, making it preferable for military uses. Still, the overall size of lidar units has to decrease before they will become ubiquitous in aircraft.
• Mars rock analysis: NASA may soon be using laser-induced spectroscopy to explore Mars. Since materials in the planet's desert environment are often very weathered, they can be coated with up to 2mm of clay and other compounds. Lasers, when applied to soil, air or water samples, burn through the weathering and evaporate samples. Because each atom emits a unique spectral signature, scientists will be able to discern the composition of samples, even when elements exist in as few as 2 parts per million.

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