At the nanoscale level, harnessing light is an exciting collision of worlds that combines theory-based experimentation with cutting-edge applications.
IEEE Member Alexandra Boltasseva’s work in nanophotonics, or light manipulation at the nanoscale level, earned her two awards this year.
The IEEE Photonics Society honored Boltasseva in June with the 2013 Young Investigator Award, presented to an individual who has made outstanding technical contributions before his or her 35th birthday. In April, she received the Materials Research Society’s 2013 Outstanding Young Investigator Award for pioneering research in advanced plasmonic, metamaterial, and optics devices. The awards came with a total prize of US $6000.
In college,“I had wanted to study elementary particle physics, like the Higgs boson, but then I realized that everything is so complex and expensive in high-energy physics that I might end up waiting decades for a result,” says Boltasseva, who turned 35 in January. “Optics excited me because it’s the technology of the future and touches all aspects of our lives.”
She is an associate professor at Purdue University, in West Lafayette, Ind., at both the school of electrical and computer engineering and the Birck Nanotechnology Center. Her research focuses on plasmonic metamaterials, which are man-made composites of metals and insulators with optical properties not found in nature. She says she’s hoping the new materials will lead to advanced optical technologies applicable to high-performance microscopes and computers, improved solar cells, and new devices for the emerging field of quantum information technology.
“One of our goals is to manipulate light effectively at the nanoscale level and to create novel optical nanodevices,” she says. “My team is striving to bring materials research and engineering into the field of plasmonic metamaterials, an expertise that is largely missing.”
Optical transmission of data is faster than wire transmission and can carry information without degradation over long distances. But finding materials that allow cost-effective and efficient operation of nanoscale optical circuits has been tricky.
The wavelengths used for optical data transmission lie in the visible and near-infrared spectrum, 500 to 1550 nanometers, too large to interact with particles whose dimensions are in the neighborhood of 10 nm. This has hindered the development of chips containing nanoscale optics circuitry. Not only can shorter wavelengths—ultraviolet and X-rays—be harmful to human beings, but current methods of generating, transporting, and detecting them are too costly and complex. So Boltasseva’s team is developing materials and metal-based nanodevices that attract and manage light waves at the nanoscale.
“The challenge is the large wavelength of light. Traditional approaches can’t focus lasers on dimensions smaller than the order of the wavelength itself,” she says. “This limits the sizes of optical integrated chips needed for the next generation of computers, because you can’t shrink the dimensions of the conventional optical interconnects and components. So our goal is to focus, guide, and route the light at the nanoscale.”
Metals at the nanoscale level support oscillations of free-floating electron clouds, which draw light to the metal nanoparticles that would otherwise pass around them. Optical nanophotonic circuits could then manipulate and control the routing of the harnessed light in devices much tinier than conventional lasers and fiber systems. The most efficient metals for that are gold and silver. But they are expensive, cannot be combined with materials used in conventional semiconductor devices, and absorb too much light.
Instead, Boltasseva and her team are developing cost-effective metamaterial devices for harnessing and controlling light that can also be integrated with today’s semiconductor materials. “We’re finding the right materials, tailoring and optimizing their properties, and making unit cells—or metamaterial ‘atoms’—out of them,” she says.
“There’s no single answer to what the best plasmonic material is,” she adds. “We’ve identified several classes of materials for specific applications, including nanoscale optical interconnects and high-sensitivity sensors, improved solar cells, and powerful microscopes capable of viewing things at nanoscale levels. Each requires different materials.”
Boltasseva’s group was able to get promising results with near-infrared wavelengths by pushing the limits of doping, a common semiconductor performance-enhancing technique in which electrons are added to a material to create additional charge and metallic properties.
Boltasseva found that adding aluminum or gallium to zinc oxide (used for display panels) donated enough free-floating electrons to create a metallic material in telecommunication wavelengths around 1500 nm. But shorter wavelengths require a different approach. That’s where alternative plasmonic materials come in.
“There’s a limit to how high you can dope semiconductors,” she notes. “You can’t get them to behave like a metal in the visible-light range, so we had to look at other materials, including metallic nitrides such as titanium nitride and zirconium nitride.” She is also looking into how to tailor and fine-tune other materials to focus and route visible light.
THE EARLY YEARS
Born in Kanash, Russia, about 700 kilometers east of Moscow, to parents who were engineers, Boltasseva tinkered with resistors, transistors, and lightbulbs as a teen, and she earned national honors in Russia’s Physics Olympics. She says it was her father and her high school physics teacher who motivated her to pursue physics and engineering.
Boltasseva graduated from the Moscow Institute of Physics and Technology, where she earned bachelor’s and master’s degrees in applied physics and mathematics in 1999 and 2000. She then earned her Ph.D. in electrical engineering in 2004 from the Technical University of Denmark (DTU), in Kongens Lyngby, just outside Copenhagen.
After brief stints as a research scientist for two start-up IT companies that manufactured optical components, she returned to DTU for a postdoctoral and faculty position. Purdue hired her in 2008 as an assistant professor of electrical and computer engineering. She was promoted this year to tenured associate professor.
Boltasseva’s more than two dozen commendations for her work include the 2011 TR35 Award, MIT Technology Review’s annual listing of 35 innovators under 35 whose work, says the magazine, is changing the world.