Researchers are developing a new class of “plasmonic metamaterials” as potential building blocks for advanced optical technologies and a range of potential breakthroughs in the field of transformation optics. This image shows the transformation optics “quality factor” for several plasmonic materials. For transformation optical devices, the quality factor rises as the amount of light “lost,” or absorbed, by plasmonic materials falls, resulting in materials that are promising for a range of advanced technologies. (Birck Nanotechnology Center, Purdue Univ.) |
Researchers are developing a new class of “plasmonic
metamaterials” as potential building blocks for advanced optical
technologies, including ultrapowerful microscopes and computers, improved solar
cells, and a possible invisibility cloak.
The new materials could make possible
“nanophotonic” devices for numerous applications, said Alexandra
Boltasseva, an assistant professor of electrical and computer engineering at Purdue Univ.
Unlike natural materials, metamaterials may possess an
index of refraction less than one or less than zero. Refraction occurs as
electromagnetic waves, including light, bend when passing from one material
into another. It causes the bent-stick-in-water effect, which occurs when a
stick placed in a glass of water appears crooked when viewed from the outside.
Being able to create materials with an index of refraction
that’s negative or between one and zero promises a range of potential
breakthroughs in a new field called transformation optics. However, development
of new technologies using metamaterials has been hindered by two major limitations:
too much light is “lost,” or absorbed by metals such as silver and
gold contained in the metamaterials, and the materials need to be more
precisely tuned so that they possess the proper index of refraction.
Now, researchers are proposing a new approach to overcome
these obstacles. Findings will be detailed in an article appearing in the
journal Science. The article was
written by Boltasseva and Harry Atwater, Howard Hughes Professor and a
professor of applied physics and materials science at the California Institute
of Technology.
The researchers are working to replace silver and gold in
materials that are created using two options: making semiconductors more
metallic by adding metal impurities to them; or adding non-metallic elements to
metals, in effect making them less metallic. Examples of these materials
include aluminum oxides and titanium nitride, which looks like gold and is used
to coat the domes of Russian churches.
Researchers have tested some of the new materials, demonstrating
their optical properties and finding that they outperform silver and gold, in
work based at the Birck Nanotechnology Center
in Purdue’s Discovery
Park.
Plasmonic metamaterials are promising for various
advances, including a possible “hyperlens” that could make optical
microscopes 10 times more powerful and able to see objects as small as DNA;
advanced sensors; new types of light-harvesting systems for more efficient
solar cells; computers and consumer electronics that use light instead of electronic
signals to process information; and a cloak of invisibility.
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.
Some of the new materials are showing promise in uses
involving near-infrared light, the range of the spectrum critical for
telecommunications and fiberoptics. Other materials also might work for light
in the visible range of the spectrum. The new materials might be tuned so that
their refractive index is ideal for specific ranges of the spectrum, allowing
their use for particular applications.
Future photonics technologies will revolve around new
types of optical transistors, switches and data processors. Conventional
computers transmit and process pieces of information in serial form, or one
piece at a time. However, future computers may use parallel streams of data,
resulting in much faster networks and computers.