Nanoantennas Form Ultrathin Holograms for Sensing

An ultrathin hologram — only 1/23rd the width of the light wavelength used to create it — could make possible light-based devices and optical switches small enough to be integrated into computer chips for advanced sensors, high-resolution displays and information processing.

The holograms were made at Purdue University using a metasurface capable of ultra-efficient control of light. Created from thousands of V-shaped nanoantennas formed into an ultrathin gold foil, the metasurface could make possible "planar photonics" devices, said Alexander Kildishev, associate research professor of electrical and computer engineering at Purdue.

Researchers have created tiny holograms using a "metasurface" capable of the ultra-efficient control of light, representing a potential new technology for advanced sensors, high-resolution displays and information processing. To demonstrate the technology, researchers created a hologram of the word Purdue smaller than 100 µm wide, or roughly the width of a human hair. Images courtesy of Xingjie Ni, Birck Nanotechnology Center.

Laser light shines through the nanoantennas, creating the hologram 10 µm above the metasurface. As a demonstration, researchers created a hologram of the word "Purdue" smaller than 100 µm wide.

"If we can shape characters, we can shape different types of light beams for sensing or recording or, for example, pixels for 3-D displays. Another potential application is the transmission and processing of data inside chips for information technology," he said. "The smallest features — the strokes of the letters — displayed in our experiment are only 1 micron wide. This is a quite remarkable spatial resolution."

Metasurfaces could make it possible to use single photons for switching and routing in future computers. While using light would dramatically speed up computers and telecommunications, conventional photonic devices cannot be miniaturized because the wavelength of light is too large to fit in tiny components needed for integrated circuits. Nanostructured metamaterials, however, are making it possible to reduce the wavelength of light, allowing the creation of new types of nanophotonic devices, said Vladimir M. Shalaev, scientific director of nanophotonics at Purdue's Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.

Laser light shines through the metasurface from below, creating a hologram 10 µm above the structure.

"The most important thing is that we can do this with a very thin layer, only 30 nanometers, and this is unprecedented," Shalaev said. "This means you can start to embed it in electronics, to marry it with electronics."

Under development for about 15 years, metamaterials owe their unusual potential to precision design on the scale of nanometers. Optical nanophotonic circuits might harness clouds of electrons called "surface plasmons" to manipulate and control the routing of light in devices too tiny for conventional lasers.

The researchers have shown how to control the intensity and phase of laser light as it passes through the nanoantennas (each antenna has its own phase delay). Controlling the intensity and phase is essential for creating working devices and can be achieved by altering the V-shaped antennas.

The findings are detailed in Nature Communications. The article was written by former Purdue doctoral student Xingjie Ni, who is now a postdoctoral researcher at the University of California, Berkeley, and by Kildishev and Shalaev.

The work is partially supported by the US Air Force Office of Scientific Research, Army Research Office, and the National Science Foundation. Purdue has filed a provisional patent application on the concept.

For more information, visit: www.purdue.edu/discoverypark/nanotechnology/