The incredible lightness of beams

Photonics - where particles of light have the potential to carry morethan 100 times the information of the electrons that run electronicdevices.

When the Federal Bureau of Investigation Laboratories wanted to find out whether O.J. Simpson really did own a pair of Bruno Magli shoes, it used some special techniques with light to see what was not otherwise visible to the human eye. Using red light to look at the now famous photos of the football star on the Buffalo Bills' football field, FBI researchers were able to see the tread of the soles clearly, and match it to the Italian shoemaker.

"We were able to compare the tread with the manufacturer's samples to confirm that it was a Bruno Magli," said Donald Kerr, director of the FBI Labs in Washington, D.C., at a recent Boston University symposium on new uses of photonics, or light technology.

But photonics travels far beyond the realm of crime-fighting. Telecommunications, photo imaging, electronic printing, medicine, and consumer electronics are all fields using photonics to improve current products and invent new ones. CD players, digital cameras, excimer lasers to correct eyesight, fiber-optic telecommunications equipment, and supermarket bar-code scanners all use photonics.

Photons, or particles of light, have the potential to carry more than 100 times the information of the electrons that run electronic devices, and they allow for much smaller components.

Researchers at the Boston University Photonics Center say photonics is poised for explosive growth, much like the electronics industry over the past 30 years. According to the Optoelectronics Industry Development Association in Washington, D. C., the market for photonics products worldwide is more than $160 billion this year. Communications products are $32 billion of that, computer disk storage products $42 billion, flat displays $44 billion, and imaging devices $20 billion.

'Smart skin' measures person's gait

The Boston University center has developed enough photonics technology to spawn three start-up companies. One of them, PhotoSense Inc., has developed a smart skin, or thin blanket of photonic sensors. The smart skin can be used to measure the foot stress and gait so people can get custom orthotics for their shoes, to monitor hospital patients, or to improve the safety of car seats.

Another company, PhotoDetection Systems Inc., has developed portable medical imaging systems that are more accurate than today's systems. And PhotoSecure Inc. has made photochemicals that can detect trace elements of contaminants in food and water and determine whether airplane parts, pharmaceuticals, and other items are counterfeit.

Photonics has become the latest weapon in the FBI's arsenal of law-enforcement tools. With lights of different wavelengths, FBI scientists can lift signatures that were crossed out, see alterations in documents, and view more details with surveillance cameras. They were even able to read letters on a murder victim's hand, spelling out the name of her killer.

There also are some futuristic photonics applications still on the lab bench at the Photonics Center, according to Shawn Burke, deputy director of the center. One is what Mr. Burke claims is the fastest photo detector in the world, a device that can sense optical signals. It will be used as a component of a next-generation telecommunications receiver that can detect and capture light signals and then convert them into electricity.

Burke says the receiver would operate at a very high bandwidth. Bandwidth is the range of frequencies or wavelengths within which information moves: the higher the bandwidth, the more information can be moved more quickly. Bandwidth is expressed in frequency, such as gigahertz, or in the case of electronic communications systems, as data transferred in bits per second. Today's telecommunications receivers operate at a maximum of 10 gigahertz. The Boston University detector can operate at full efficiency at 50 gigahertz, and at 50 percent efficiency (which Burke says still is adequate) at 100 gigahertz.

The traditional way to increase bandwidth is to capture more photons to turn into electricity. This is done by thickening the layers of semiconductor materials that capture the light and convert it into electricity. But making fatter layers also slows down the photons. So to keep the layers thin, the Boston University scientists built into their detector a series of mirror-like devices that reflect light and keep it bouncing until it is absorbed into the semiconductor materials.

"This increases the chance that the photon will be captured, but it does not sacrifice the speed," Burke says.

The detector and other devices will be crucial as current electronics technologies run out of steam, Burke says. In a recent article in Science magazine, Paul Packan, a scientist at Intel Corp., a leading computer microchip company, says there now is a physical limit to how small an electronic transistor can be made.

In the past 30 years, transistors were miniaturized so quickly that every 18 months, the number of transistors that fit onto a silicon microchip doubled. That means the microchip also became twice as powerful. This principle is known as Moore's Law, after Intel founder Gordon Moore. Mr. Packan says the generation of microchips to be released next year may be the beginning of the end of Moore's law.

This is where photonics can replace or extend existing electronics technology. Burke says Moore's Law already is outdated in a branch of advanced telecommunications known as wave-division multiplexing, a technology that greatly speeds information transmission and expands bandwidth.

"The bandwidth capacity is getting to the point where the processing devices at either end of the fiber-optic line can't keep up with the information on the line," Burke says. Computers and other information processing devices take electricity and convert it to a light signal that can travel over a fiber-optic cable, and they then reconvert the light to electricity at the other end of the transmission line.

The Internet is driving much of the demand by businesses and consumers for more information more quickly, which translates into more bandwidth. It took 75 years for telephones to be used by 50 million customers, but it took only four years for the Internet to reach that many users, says Thomas Koch, chief technical officer at Lucent Technologies in Murray Hill, N.J. (Bell Labs is the research arm of Lucent.)

"Optical fiber is being deployed worldwide at a rate of Mach 3. That's fast enough to circle the globe twice a day," Mr. Koch says. "And there's a doubling of fiber-optic capacity every nine to 12 months. We'll get into multiple terabit [trillions of bits] bandwidths soon in the next century." Most of today's telecommunications lines operate in the gigabits (billions of bits) per second range.

Koch says, however, that technologies to make components and manufacturing equipment for photonics still need to be improved to add functions and trim cost.

Lighting is $12 billion market

Lighting, naturally, also is a large application for photonics. The current global market for traditional lamps, including incandescent and fluorescent bulbs, is worth $12 billion, and newer lighting devices like LEDs for electronics equipment are another $4 billion, says William Jackson, vice president of technology for GELcore LLC, an Independence, Ohio, maker of lamps and LEDs.

Current LEDs typically are red, orange, and yellow. They are used in everything from computer equipment to traffic lights, automobile signals, and the brake lights on Federal Express trucks. Newer technologies are being used to make brighter green, blue, and white LEDs that use less energy. Such LEDs could last 10 to 100 times longer than current lamps. But currently, they cost double the cost of traditional technologies. It will take years before the technology is mature enough to be affordable and attractive to consumers.

But the promise of superbright LEDs is enormous, says Burke. "Thirty percent of the world's energy goes into lighting. If we could get a bright white light source using half the energy, we could cut lighting to half of the world's energy use."

Photographic companies like Eastman Kodak in Rochester, N.Y., also are excited about the promise of photonics. Kodak is developing film and cameras that work with computers so that people can share photos of their family and friends via the Internet or electronic mail, and then print them out on computer printers. Carl Kohrt, Kodak's chief technical officer, says such technologies are expensive now, but they will come down in price in the future.

"Photonics technology is the key to unlocking the potential of many areas of imaging," Mr. Kohrt says.

While photonics technology can help people like law enforcers, it also creates problems. For example, evidence presented in court must be original, and witnesses must be able to document where the evidence was at all times. Digital photography makes this hard, because an original digital photo can be reproduced repeatedly with no degradation of quality, and it can be altered and enhanced easily.

Says the FBI's Kerr, "Our new challenge is to detect image manipulation."

(c) Copyright 1999. The Christian Science Publishing Society

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