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FEATURE
Light Fantastic - The potential of photonics and optics is just starting to be tapped. + By Thomas K. Grose

If you ever visit the Florida Atto Science and Technology lab at the University of Central Florida during a laser-pulse investigation, don’t blink. You might miss a few billion of them. A research team there recently set the record for the world’s shortest laser pulses — 67 attoseconds, or quintillionths a second, of extreme ultraviolet light—and devised a blazingly fast camera to capture the flashes. Investigators now will be able literally to photograph the mechanics of quantum mechanics. “We’ll see atomic phenomena in action,” enthuses Bahaa Saleh, dean of UCF’s College of Optics and Photonics. Equally notable: The feat didn’t require a particle accelerator, huge synchrotron, or other specialized equipment.

Efforts to compress laser pulses into unfathomably brief bursts are just one aspect of the pioneering work that engineers are conducting in the emerging field of optics and photonics — the science and manipulation of light. Since ancient times, this frontier of discovery has captivated some of the world’s greatest minds — including physicists David Wineland and Serge Haroche, who earned the 2012 Nobel Prize in physics for their groundbreaking research using light to manipulate, control, and observe subatomic particles without destroying them. Their work could lead to quantum computers and superprecise clocks — “the future basis for a new standard of time,” in the words of the Royal Swedish Academy of Sciences.

Society already reaps the benefits from photonics and optics engineering. Optical fiber networks literally crisscross the globe, transmitting phone calls, video, and other data along a superhighway of photons. Indeed, the call from Stockholm to Wineland at his home in Boulder, Colo., where he works at the National Institute of Standards and Technology, was carried over optical fibers. Without fiber optics, the Internet would not exist, let alone allow Google to process 4.6 billion searches a day or YouTube to upload an hour’s worth of videos every second. The smartphone is a hand-held testament to optics, from the lithography used to etch its integrated circuits, to its camera’s sensor and lens, to its touch-screen display (backlit by LEDs), to the lasers that carved its shell from ferrous and nonferrous materials. Additionally, CDs, printers, scanners, computers, and many medical imaging devices and therapies are optics based.

“It affects nearly all things in our lives,” says Saleh, who predicts optics will spawn myriad wondrous devices and products, from ultrafast computers to cheaper solar cells and superthin display screens as flexible as paper “that will kill the print industry within the decade.”

Such is the field’s industrial and job-growth potential that a National Academies panel has called for a National Photonics Initiative to develop a coherent, multiagency research-and-development strategy and keep the United States ahead of the curve.

The economic impact of optics has been hard to measure, in part because the technology is “used in devices to facilitate the objective of the end device, rather than being an end device,” explains Xi-Cheng Zhang, director of the Institute of Optics at the University of Rochester. But the White House Office of Science and Technology Policy has reported that in 2009 and 2010, for instance, some $4.9 billion worth of lasers were sold in the United States; their deployment in the transportation, biomedical, and telecommunications sectors ultimately contributed $7.5 trillion to America’s GDP.

“Once we had lasers, we had concentrated power.” – Bahaa Saleh, dean of the College of  Optics and Photonics at the University of Central Florida

 

Galiled To Einstein

Optics and photonics are generally interchangeable terms. Technically, optics is the science of generating and propagating light. Photonics is the engineering application of that science, or the detection, transmitting, and processing of light. The field dates back to ancient Egypt and has fascinated many of the greatest names in science, including Galileo, Newton, and Einstein. In the 1940s and ’50s, it was mainly associated with lenses: microscopes, telescopes, cameras. That changed in 1960 with the first laser beam. “Once we had lasers, we had concentrated power,” Saleh says. Since then, the field has grown to include optical fibers and solid state electronics, key to the creation of ever faster, smaller computer chips as well as the long-lasting LED and OLED lights that soon will largely replace the incandescent bulb.

Meanwhile, the concentrated power of lasers was quickly put to use in a variety of ways. Manufacturers initially used lasers to cut metal. Today, some of the 3-D printers used in additive manufacturing are laser based — as are the short pulses of light that zip data through optical fibers. Laser light also is crucial to unlocking the mysteries of the atom. Zenghu Chang, a professor of physics and optics at Central Florida University whose team achieved the world’s shortest laser pulse, created an even faster camera to measure it, allowing scientists to see quantum mechanics in action.

Researchers say that consumer electronics could soon give way to consumer photonics, given ongoing efforts to create optical chips. Today’s microprocessors use electricity to transfer data, which means all information that now flows into computers as pulses of light via optical fibers must be converted to current. But electrons move at only 10 percent the speed of light, creating bottlenecks that slow computations. To speed things up, researchers want to build optical silicon chips that transmit data via lasers, so the entire process operates with photons.

MIT’s Caroline Ross, a professor of materials science and engineering, is at least partway there with a crucial piece of a silicon optical chip: a “diode for light.” The diode ensures that the light from lasers will travel in only one direction. “You need that to protect the laser from having light going back into it,” Ross says. “If there’s a lot of reflection back into the laser, it becomes unstable.” Her team uses garnet, which transmits light differently depending on which direction it comes from. Light coming into a chip the wrong way gets diverted by the thin film of garnet to a loop outside the light transmission channel. Acknowledging that “lasers are at the primitive stages right now,” Ross nevertheless remains optimistic that optical chips are in our future.

Trillion, trillion, trillion’

So are quantum computers, thanks in part to Nobel laureates Wineland and Haroche. Computers today perform calculations using binary sequences of 0s and 1s, represented by electrons. Quantum computers instead manipulate atoms or molecules to take advantage of such quantum mechanical properties as superposition, which means a particle can be in two states at the same time. (Even Einstein found the phenomenon “spooky.”) Superposition means quantum bits, or qubits, can run almost endless calculations simultaneously while an electronic computer runs one, because each additional qubit doubles the amount of possible states. According to Rochester physicist Adam Frank, writing recently in the New York Times, a machine using 300 qubits “would be a million, trillion, trillion, trillion times faster than the most modern supercomputer.”

What’s that got to do with optics? A team at the University of Bristol’s Center for Quantum Photonics in England recently developed a breakthrough quantum chip using photons. “Light is a very good information carrier,” explains Mark Thompson, the center’s deputy director. Because a mere 100 photons could do trillions of calculations simultaneously, a quantum computer could complete in six months a problem that would take a classical supercomputer “the age of the universe,” Thompson says. That’s so fast that a quantum computer just one tenth that size would still be speedy. In fact, Thompson’s team—which has “demonstrated all the key elements” working with three or four photons at a time—expects to have a 10-photon computer that can work at room temperature ready to “challenge” electronic supercomputers within three years. Thompson predicts 30- to 100-photon quantum computers lie just a decade away, though most estimates put the time frame at 25 to 30 years. The next big hurdle: regenerating photons on a single chip. Once built, quantum computers would be powerful tools to simulate molecules, as well as pharmaceuticals and materials that now remain out of reach of today’s supercomputers. They particularly would excel at pattern recognition and database searches.

Gas cell where the attosecond light is emitted. Courtsey of Dr. Zenghu Chang

Medicine already depends heavily on optics: X-rays and CAT scans, for instance. And lasers are quickly becoming the therapy of choice for treating kidney stones. But optics is poised to grow. Paul French, head of the Photonics Group at London’s Imperial College, is working on imaging technologies based on spectrometers that one day could differentiate between cancerous and healthy tissue, a key to targeting treatments. While progress is being made, scattering and absorption of optical radiation by tissue can cause images to degrade. Rochester’s Zhang, who leads his institute’s terahertz (THz) R&D program, sees many potential medical and homeland security uses for THz signals. Researchers believe THz time-domain spectroscopy might also be used to pick out characteristics unique to explosives and narcotics.

To a generation familiar with cartoon characters brandishing ray guns, a weapon under development by the Army might look familiar. It literally shoots bolts of lightning by manipulating ultra-short laser pulses. The Air Force wants to develop drones — unmanned aerial vehicles — that take inspiration from insects, crustaceans, and spiders. Current drones use optical sensors that work like human eyes, which limits their capability. Bug eye-inspired vision systems that take advantage of more of the light spectrum could allow for better detection, recognition, and tracking of targets.

Optics and photonics research is also directed at improving technology that transforms sunlight into electricity and cutting the costs of solar cells. Paul McManamon, technical director of the Ladar and Optical Communications Institute at the University of Dayton, predicts that solar power will cost no more than electricity generated from coal, gas, or oil-fired plants by 2020. “Eventually, we won’t have to subsidize” the industry, he says.

Increasing reliance on optics and photonics technology is not cost free. One problem the nation will soon face is strain on communications networks that depend on optical fibers. “Initially with optical fibers we had almost unlimited bandwidth,” French says, “but now we’re running out.” McManamon says bandwidth capacity must expand by a factor of 100 over the coming decade. “Right now, we don’t know how to do that,” he says, “but I think we’ll manage to keep it going. I’m an optimist.” And why not? When it comes to optics and photonics, the future seems so bright we’ll all need to wear shades.

 

Thomas K. Grose is Prism’s chief correspondent, based in London.

 

The attosecond streak camera for charactering the attosecond pulses. Courtsey of Dr. Zenghu Chang

 


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