Novel semiconductor structure bends light 'wrong' way -- the right direction for many applications

Oct 14, 2007
Novel semiconductor structure bends light 'wrong' way
An easy-to-produce material made from the stuff of computer chips has the rare ability to bend light in the opposite direction from all naturally occurring materials. The semiconductors that constitute the Princeton invention are grown from crystals using common manufacturing techniques, making it less complex, more reliable and easier to produce than other metamaterials. Credit: Keith Drake

A Princeton-led research team has created an easy-to-produce material from the stuff of computer chips that has the rare ability to bend light in the opposite direction from all naturally occurring materials. This startling property may contribute to significant advances in many areas, including high-speed communications, medical diagnostics and detection of terrorist threats.

The new substance is in a relatively new class of materials called "metamaterials," which are made out of traditional substances, such as metals or semiconductors, arranged in very small alternating patterns that modify their collective properties. This approach enables metamaterials to manipulate light in ways that cannot be accomplished by normal materials.

Previous metamaterials were two-dimensional arrangements of metals, which limited their usefulness. The Princeton invention is the first three-dimensional metamaterial constructed entirely from semiconductors, the principal ingredient of microchips and optoelectronics.

"To be useful in a variety of devices, metamaterials need to be three-dimensional," said Princeton electrical engineering professor Claire Gmachl, one of the researchers on the study. "Furthermore, this is made from semiconductors, which are extremely functional materials. These are the things from which true applications are made."

The research team, led by Princeton engineering graduate student Anthony Hoffman, will publish its findings online Oct. 14 in the journal Nature Materials. Other Princeton researchers on the team include graduate students Leonid Alekseyev, Scott Howard and Kale Franz; former Council of Science and Technology fellow Dan Wasserman, now at the University of Massachusetts-Lowell; and former electrical engineering professor Evgenii Narimanov, now at Purdue University. The team also includes collaborators from Oregon State University and telecommunications firm Alcatel-Lucent.

Light waves and other forms of electromagnetic radiation bend whenever they pass from one medium to another. This phenomenon, called refraction, is readily observable when a straw placed into a glass of water appears to be bent or broken. Lenses in reading glasses or a camera work because of refraction.

All materials have an index of refraction, which measures the degree and direction that light is bent as it passes through them. While materials found in nature have positive refractive indices, the material recently invented by Princeton researchers has a negative index of refraction.

In the case of the straw in a glass, normal water would make the underwater portion of the straw appear to bend toward the surface. If water were able to refract light negatively, as the newly invented semiconductor does, the segment of straw under the water would appear as if it were bending away from the surface

Far more than a neat optical illusion, negative refraction holds promise for the development of superior lenses. The positive refractive indices of normal materials necessitate the use of curved lenses, which inherently distort some of the light that passes through them, in telescopes and microscopes. Flat lenses made from materials that exhibit negative refraction could compensate for this aberration and enable far more powerful microscopes that can "see" things as small as molecules of DNA.

In addition, the Princeton metamaterial is capable of negative refraction of light in the mid-infrared region, which is used in a wide range of sensing and communications applications. Its unique composition results in less lost light than previous metamaterials, which were made of extremely small arrangements of metal wires and rings. The semiconductors that constitute the new material are grown from crystals using common manufacturing techniques, making it less complex, more reliable and easier to produce.

"Currently, the typical infrared lens is a massive object -- the setups are bulky," Hoffman said. "This new material may enable more compact mid-infrared optics because we now have a new material with an entirely new set of optical parameters in our toolkit."

The research is part of a multi-institutional research center called Mid-Infrared Technologies for Health and the Environment (MIRTHE). Researchers at MIRTHE are developing compact sensors that detect trace amounts of gases in the atmosphere and human breath. These could one day be used in devices that monitor air quality and enhance homeland security, as well as in non-invasive and on-the-spot medical tests for diabetes and lung disease.

The research relies on a new type of laser that emits mid-infrared light. Gmachl, who directs the MIRTHE project, said the new material could be used to make the lasers better and smaller.

Next, the team plans to incorporate the new metamaterial into lasers. Additionally, the researchers will continue to modify the material in attempts to make features ever smaller in an effort to expand the range of light wavelengths they are able to manipulate.

Source: Princeton University

Explore further: Modification of structural composite materials to create tailored lenses

add to favorites email to friend print save as pdf

Related Stories

Researchers steer light in new directions

Sep 16, 2013

A team of researchers led by San Francisco State University's Weining Man is the first to build and demonstrate the ability of two-dimensional disordered photonic band gap material, designed to be a platform ...

Recommended for you

Novel technique opens door to better solar cells

Apr 14, 2014

A team of scientists, led by Assistant Professor Andrivo Rusydi from the Department of Physics at the National University of Singapore's (NUS) Faculty of Science, has successfully developed a technique to ...

Probing metal solidification nondestructively

Apr 14, 2014

(Phys.org) —Los Alamos researchers and collaborators have used nondestructive imaging techniques to study the solidification of metal alloy samples. The team used complementary methods of proton radiography ...

Glasses strong as steel: A fast way to find the best

Apr 13, 2014

Scientists at Yale University have devised a dramatically faster way of identifying and characterizing complex alloys known as bulk metallic glasses (BMGs), a versatile type of pliable glass that's stronger than steel.

User comments : 0

More news stories

CERN: World-record current in a superconductor

In the framework of the High-Luminosity LHC project, experts from the CERN Superconductors team recently obtained a world-record current of 20 kA at 24 K in an electrical transmission line consisting of two ...

Glasses strong as steel: A fast way to find the best

Scientists at Yale University have devised a dramatically faster way of identifying and characterizing complex alloys known as bulk metallic glasses (BMGs), a versatile type of pliable glass that's stronger than steel.

ESO image: A study in scarlet

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

First direct observations of excitons in motion achieved

A quasiparticle called an exciton—responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits—has been understood theoretically for decades. But exciton movement within ...

Warm US West, cold East: A 4,000-year pattern

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...