Novel negative-index metamaterial that responds to visible light designed

Apr 22, 2010
Arrays of coupled plasmonic coaxial waveguides offer a new approach by which to realize negative-index metamaterials that are remarkably insensitive to angle of incidence and polarization in the visible range. Credit: Caltech/Stanley Burgos

A group of scientists led by researchers from the California Institute of Technology has engineered a type of artificial optical material—a metamaterial—with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the "wrong" direction from what normally would be expected, irrespective of the angle of the approaching light.

This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal , is simpler than previous NIMs—requiring only a single functional layer—and yet more versatile, in that it can handle with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the , making it "the first negative index metamaterial to operate at visible frequencies," says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Frontier Research Center at Caltech and the paper's first author.

"By engineering a metamaterial with such properties, we are opening the door to such unusual—but potentially useful—phenomena as superlensing (high-resolution imaging past the ), invisibility cloaking, and the synthesis of materials index-matched to air, for potential enhancement of light collection in solar cells," says Harry Atwater, Howard Hughes Professor and professor of applied physics and materials science, director of Caltech's Resnick Institute, founding member of the Kavli Nanoscience Institute, and leader of the research team

What makes this NIM unique, says Burgos, is its engineering. "The source of the negative-index response is fundamentally different from that of previous NIM designs," he explains. Those previous efforts used multiple layers of "resonant elements" to refract the light in this unusual way, while this version is composed of a single layer of silver permeated with "coupled plasmonic waveguide elements."

Surface plasmons are light waves coupled to waves of electrons at the interface between a metal and a dielectric (a non-conducting material like air). Plasmonic waveguide elements route these coupled waves through the material. Not only is this material more feasible to fabricate than those previously used, Burgos says, it also allows for simple "tuning" of the negative-index response; by changing the materials used, or the geometry of the waveguide, the NIM can be tuned to respond to a different wavelength of light coming from nearly any angle with any polarization. "By carefully engineering the coupling between such waveguide elements, it was possible to develop a material with a nearly isotopic refractive index tuned to operate at visible frequencies."

This sort of functional flexibility is critical if the material is to be used in a wide variety of ways, says Atwater. "For practical applications, it is very important for a material's response to be insensitive to both incidence angle and polarization," he says. "Take eyeglasses, for example. In order for them to properly focus light reflected off an object on the back of your eye, they must be able to accept and focus light coming from a broad range of angles, independent of polarization. Said another way, their response must be nearly isotropic. Our metamaterial has the same capabilities in terms of its response to incident light."

This means the new metamaterial is particularly well suited to use in solar cells, Atwater adds. "The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle that could enhance light collection in solar cells," he explains. "And the fact that the metamaterial has a wide-angle response is important because it means that it can 'accept' light from a broad range of angles. In the case of , this means more light collection and less reflected or 'wasted' light."

"This work stands out because, through careful engineering, greater simplicity has been achieved," says Ares Rosakis, chair of the Division of Engineering and Applied Science at Caltech and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering.

Explore further: Researchers seek broadband/multiband electromagnetic absorbers based on plasmonic and metamaterial structures

More information: "A single-layer wide-angle negative index metamaterial at visible frequencies," Nature Materials, April 2010.

Related Stories

Practical Cloaking Devices On The Horizon?

Aug 10, 2008

(PhysOrg.com) -- Invisibility cloaks get a step closer to realization, with the demonstration of a new material that can bend (visible) light the 'wrong' way for the first time in three dimensions.

Negative Index Materials: From Theory to Reality

Jun 06, 2006

Kent State University researchers are leading a team of scientists from eight institutions, who have been awarded a $5.5 million Multidisciplinary University Research Initiative (MURI) from the Air Force Office of Scientific ...

Beyond the looking glass...

Aug 13, 2009

While the researchers can't promise delivery to a parallel universe or a school for wizards, books like Pullman's Dark Materials and JK Rowling's Harry Potter are steps closer to reality now that researchers ...

Stars Locations are Uncertain

Aug 05, 2004

Whether viewed dimly through the haze and lights of a city or in all their glory in a pristine wilderness, the stars that surround the Earth are magnificent, and one day Earthlings will travel to some of the ...

Recommended for you

Study finds physical link to strange electronic behavior

10 minutes ago

Scientists have new clues this week about one of the baffling electronic properties of the iron-based high-temperature superconductor barium iron nickel arsenide. A Rice University-led team of U.S., German ...

Refocusing research into high-temperature superconductors

12 hours ago

Below a specific transition temperature superconductors transmit electrical current nearly loss-free. For the best of the so-called high-temperature superconductors, this temperature lies around -180 °C – a temperature ...

MRI for a quantum simulation

18 hours ago

Magnetic resonance imaging (MRI), which is the medical application of nuclear magnetic resonance spectroscopy, is a powerful diagnostic tool. MRI works by resonantly exciting hydrogen atoms and measuring ...

50-foot-wide Muon g-2 electromagnet installed at Fermilab

18 hours ago

One year ago, the 50-foot-wide Muon g-2 electromagnet arrived at the U.S. Department of Energy's Fermi National Accelerator Laboratory in Illinois after traveling 3,200 miles over land and sea from Long Island, ...

User comments : 10

Adjust slider to filter visible comments by rank

Display comments: newest first

mlange
5 / 5 (1) Apr 22, 2010
Finally, I can get my invisibility cloak. But seriously, I love it when things once thought impossible come to fruition.
Oliver_k_Manuel
not rated yet Apr 22, 2010
material with a nearly isotopic refractive index tuned to operate at visible frequencies."

isotropic?
Bloodoflamb
1 / 5 (1) Apr 22, 2010
material with a nearly isotopic refractive index tuned to operate at visible frequencies."

isotropic?

In general, an index of refraction is a second rank tensor with directional dependence. Scalar refractive indices are typically only approximations.
Hunnter
5 / 5 (1) Apr 23, 2010
This is fantastic news!
Metamaterials might come along for consumer use much sooner than was predicted.

I'm predicting they will extend to the rest of the visible spectrum before years end.
I sure hope they do that is.

EM blackholes will be a whole new department of research, much more efficient than regular solar cells and the like.
Of course, to prevent scaring the average person, EM Hole would be better. LHC was bad enough in scaring half the planet when blackhole was mentioned...
theophys
5 / 5 (2) Apr 23, 2010
Of course, to prevent scaring the average person, EM Hole would be better. LHC was bad enough in scaring half the planet when blackhole was mentioned...


yea...that was a fun couple of years. Nothing like explaining that particle accelerators can't destroy the planet over and over to completely destroy your faith in humanity.
vidyunmaya
1 / 5 (1) Apr 24, 2010
Blackhole is a misnomer-Electromagnetic Wave guide helps to retrieve Energy. LHC concepts are wrong and mislead Spirit of Science.
Hearty congratulations for the team spirit
Vidyardhi Nanduri [Cosmology Vedas Interlinks]
Ronan
not rated yet Apr 24, 2010
Spiffiness! I know full well that there's plenty that one could do with metamaterials for longer wavelengths, but...my little human selfishness still can't help but be ecstatic to finally have some of this weirdness that I can actually SEE (or not see, in the case of invisibility cloaks). Excellent news.
bluehigh
1 / 5 (1) Apr 25, 2010
If this can be made practical, expect its to be outlawed. Probably already is if used to disguise your identity.

Where did I put my invisibilty cloak. Not much point in looking for it I suppose.
PinkElephant
not rated yet Apr 25, 2010
"The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle metamaterials that could enhance light collection in solar cells," he explains.
I wonder how they make the jump from optimizing a particular frequency, to broadband.
Coldstatic
not rated yet Apr 26, 2010
im going to assume that they mean setting up an array of differently 'tuned' metamaterials. I wonder what would happen if stacked them