Researchers from the University of Würzburg have developed an electrically driven nanoscale antenna that generates directed infrared light. The technology could be used to exchange data between different processor cores with little loss and at the speed of light. The antenna, called a Yagi Uda antenna, was developed by the nano-optics working group of professor Bert Hecht. The name “Yagi-Uda” is derived from the two Japanese researchers who invented the antenna in the 1920s, Hidetsugu Yagi and Shintaro Uda. “Basically, it works in the same way as its big brothers for radio waves,” said Dr. René Kullock, a member of the nano-optics team. The world's first electrically powered Yagi-Uda antenna was built at the University of Würzburg's Department of Physics. Courtesy of the Department of Physics at Julius-Maximilians-Universität. An AC voltage is applied that causes electrons in the metal to vibrate and the antennas to radiate electromagnetic waves. “In the case of a Yagi-Uda antenna, however, this does not occur evenly in all directions but through the selective superposition of the radiated waves using special elements — the so-called reflectors and directors,” Kullock said. “This results in constructive interference in one direction and destructive interference in all other directions.” Applying the laws of antenna technology to nanometer-scale antennas that radiate light is technically challenging. Previously, the Würzburg physicists were able to demonstrate that the principle of an electrically driven light antenna works. But to make a relatively complex Yagi-Uda antenna, they had to come up with some new ideas. In the end, they succeeded thanks to a sophisticated production technique. “We bombarded gold with gallium ions which enabled us to cut the antenna shape with all reflectors and directors as well as the necessary connecting wires from high-purity gold crystals with great precision,” Hecht said. The researchers then positioned a gold nanoparticle in the active element so it touches one wire of the active element while keeping a distance of only one nanometer to the other wire. “This gap is so narrow that electrons can cross it when voltage is applied using a process known as quantum tunneling,” Kullock said. This charge motion generates vibrations with optical frequencies in the antenna, which are emitted in a specific direction thanks to the special arrangement of the reflectors and directors. “This has allowed us to build the world’s smallest electrically powered light source to date that is capable of emitting light in a specific directions,” Hecht said. The antenna will need further development before it is used in practice. The physicists will have to work on the antenna’s counterpart that receives light signals. The signal’s efficiency and stability will also need to be improved. The research was published in Nature Communications (www.doi.org/10.1038/s41467-019-14011-6).