Steered Light Could Replace Lasers for Military, Commercial Applications

As a red beam of light is reflected in an arch, Prasad Iyer, right, and Igal Brener demonstrate optical hardware used for beam steering experiments at Sandia National Laboratories’ Center for Integrated Nanotechnologies.

Sandia National Laboratories photo

Sandia National Laboratories recently made a breakthrough that could lay the groundwork for replacing power-hungry laser beams with ordinary light.

Two lab research scientists, Igal Brener and Prasad Iyer, proved it’s possible to steer light from conventional sources like light bulbs or flashlights.

“We’ve shown a proof of principle that incoherent light emissions can be dynamically steered,” Iyer explained.

The technology could be used in applications ranging from remote sensing and holographic displays to high-speed communications.

Incoherent light is the diffused or scattered light produced by familiar devices such as incandescent and LED bulbs. Coherent light is the focused light produced by lasers. Until last November, experts in nanophotonics and ultra-fast optics considered it impossible to dynamically steer incoherent light.

Brener and Iyer achieved the breakthrough by embedding light emitters called quantum dots in artificially structured material known as a “metasurface” on a reflective mirror.

Quantum dots have been known of in the semiconductor field for decades, Brener said. “It’s only now that they are being applied practically.

For example, you have quantum dot screens for TVs. There are companies now making micro-LED displays that utilize a different type of quantum dot.”

Iyer described the metasurface as an extremely thin optical element which recreates the refractive properties — the ability to bend and focus light — of the curved lenses found in cameras or the human eye in a “flat nanostructure at submicron thickness.”

Comprising meta-atoms — the miniscule components semiconductors are made from — metasurfaces are capable of reflecting light with amazing efficiency. Research using metasurfaces to help steer light rays has been undertaken before but presented a challenge because these artificial structures had only been designed for coherent light sources.

Working in the Center for Integrated Nanotechnologies facility at Los Alamos National Laboratory, the researchers paired the metasurface, quantum dots and reflective mirror with a spatial light modulator.

The modulator “structured an optical pulse generated separately,” according to Iyer, and projected it onto the metasurface to change the way the surface reflected light by dynamically steering the ultra-fast quantum dot emissions. Brener and Iyer found that the light waves could be focused and steered over a 70-degree range for about a trillionth of a second — long enough to confirm that incoherent light can be steered.

Iyer said creating a spatial structure on the optical pulse “translates into a spatial refractive index profile which determines the angle of light emission from the metasurface.”

The same spatial refractive index profile could be generated using “electrically tunable methods,” a goal the two researchers are working toward with an eye to producing ultra-fast beam steering devices with low power requirements for commercial and military applications, Iyer said.

Brener said Sandia already has interest in the technology from private sector companies and added that a range of adaptations are possible for the defense sector.

The technique could be applied for low-power displays that overlay maps, blueprints or other information on helmet visors or goggles. Steering incoherent light could also yield small, low-power displays capable of projecting holographic images onto human eyeballs using low-power LEDs. That would be relevant for augmented and virtual reality devices for training or operational missions.

Redirecting and focusing incoherent light beams has promise too in devices where light detection and ranging sensors are used to detect objects, LIDAR for example. Radio frequency manipulation for high-speed communications is another possibility, Brener added.

Funded by the Department of Energy, the Sandia team working on ultra-fast beam steering consisted of fewer than 15 members. With additional researchers and more resources, Brener estimated that devices employing the technology could be practical in five to 10 years.

Notionally, they would include a very thin optical or pixel element consisting of a metasurface with embedded light emitters, quantum dots for example, powered electrically. The small, lightweight, low-power optical element could be flexible enough to satisfy a range of operating speeds and beam power needs.

“It wouldn’t have a large footprint,” Iyer noted. “You can imagine AR or VR displays where you need everything very compact, where you can’t afford bulk optics.”

Topics: Emerging Technologies