Nanolaser Uses Atomically Thin Gain Medium

With potential for on-chip optical communications applications, a tungsten-based nanoscale laser operates reliably on a tiny amount of electricity.

Developed by researchers at the University of Washington and Stanford University, the device incorporates a photonic crystal cavity with a monolayer of tungsten diselenide.

“This is a recently discovered, new type of semiconductor which is very thin and emits light efficiently,” said Washington doctoral candidate Sanfeng Wu. “Researchers are making transistors, light-emitting diodes and solar cells based on this material because of its properties. And now, nanolasers.”

Operating at 130 K, the nanolaser requires pump energy of only 27 nW. Its small size and low operating energy make it a good candidate for use in photonic integrated circuits, the researchers said.

An ultrathin semiconductor stretches across the top of the photonic cavity. Courtesy of the University of Washington.

Meanwhile, they said using a separate atomic sheet as the laser gain medium offers versatility and the opportunity to more easily manipulate the laser’s properties.

“When you're working with other materials, your gain medium is embedded and you can’t change it,” said Washington professor Dr. Arka Majumdar. “In our nanolasers, you can take the monolayer out or put it back, and it's much easier to change around.”

Specifically the WSe₂ monolayer confines direct-gap excitons to within 1 nm of the cavity surface. The material also allows flexible laser operation through external controls such as electrostatic gating and current injection.

Another type of nanolaser involves quantum dots embedded in a photonic crystal cavity, but the random positions and compositional fluctuations of the dots, difficulty in current injection, and lack of compatibility with electronic circuits has limited these lasers’ practical applications, researchers said.

Funding came from the U.S. Air Force Office of Scientific Research, Office of Naval Research, National Science Foundation, Department of Energy, European Commission and the state of Washington’s Clean Energy Institute.

The research was published in Nature (doi: 10.1038/nature14290).

For more information, visit www.washington.edu.