Tiny computer microchips can hold immense computing power, thanks to the marvel of electronic integrated circuits which are printed down to the nanometer. But as these devices shrink, the physical constraints of supplying energy to and removing heat from chips become harder to overcome. As such, researchers around the world are looking to develop futuristic devices based on photonics, which manipulate light instead of electrons to perform computations.
However, the development of compact photonics to rival electronic microchips requires semiconductor lasers that can generate strong light while taking up little space. A group of scientists led by Arseniy Kuznetsov, a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE), has invented a novel nanoantenna chain that fits in a small space and delivers laser light horizontally, making it perfect for developing photonic microchips.
“The ‘nanoantennas’ we work with are tiny etched cylinders, which interact resonantly with light because their size is comparable to the wavelength of light,” explained Kuznetsov, whose team has successfully built lasers from two-dimensional arrays of nanoantennas. However, those designs emitted light vertically, away from the nanoantennas rather than along them, and so were less suited for photonics applications that require light to be manipulated along the surface of a microchip.
Instead, computational modeling by colleagues at A*STAR’s Institute of High Performance Computing (IHPC) showed that light could resonate along a one-dimensional chain of nanoantennas and be emitted at either end. Kuznetsov and his team then built prototype ‘nanochains,’ each containing a hundred nanoantennas, using gallium arsenide, a common material for converting input energy into laser light output. They found that these nanochains indeed formed successful lasers when illuminated with pump light.
“Compared to a competing state-of-the-art nanowire laser, our nanochain laser only required one-tenth as much input energy to emit laser output, while occupying only one-quarter of the area,” Kuznetsov said. Furthermore, Kuznetsov and his team discovered that they could control the direction of laser output, as off-center illumination caused laser emission from only the illuminated end of the nanochain, while illuminating the center of the nanochain resulted in lasing from both ends.
“We have successfully demonstrated the first on-chip nanoantenna chain laser and also showed that we can control the directionality of the emitted laser,” Kuznetsov said. However, he noted that the current prototype has important limitations, such as only operating at cryogenic temperatures. He and his team are currently working to improve the efficiency of the nanochain laser so that it can eventually be powered by electrical excitation instead of light.
The A*STAR researchers contributing to this work are from the Institute of Materials Research and Engineering (IMRE) and Institute of High Performance Computing (IHPC).