Skip to main content

New metamaterial gives light a one-way ticket



This is a schematic of NIST's one-way metamaterial. Forward traveling green light (left) or red light passes through the multilayered block and comes out at an angle due to diffraction off of grates on the surface of the material. Light traveling in the opposite direction (right) is almost completely filtered by the metamaterial and can't pass through. Credit: Xu/NIST

The light-warping structures known as metamaterials have a new trick in their ever-expanding repertoire. Researchers at the National Institute of Standards and Technology (NIST) have built a silver, glass and chromium nanostructure that can all but stop visible light cold in one direction while giving it a pass in the other. The device could someday play a role in optical information processing and in novel biosensing devices.


In recent years, scientists have designed nanostructured materials that allow microwave or infrared  to propagate in only one direction. Such structures hold potential for applications in optical communication—for instance, they could be integrated into photonic chips that split or combine signals carried by light waves. But, until now, no one had achieved one-way transmission of visible light, because existing devices could not be fabricated at scales small enough to manipulate visible light's short wavelengths. (So-called "one-way mirrors" don't really do this—they play tricks with relative light levels.)
To get around that roadblock, NIST researchers Ting Xu and Henri Lezec combined two light-manipulating nanostructures: a multi-layered block of alternating silver and glass sheets and metal grates with very narrow spacings.
The silver-glass structure is an example of a "hyperbolic" metamaterial, which treats light differently depending on which direction the waves are traveling. Because the structure's layers are only tens of nanometers thick—much thinner than visible light's 400 to 700 nanometer wavelengths—the block is opaque to visible light coming in from outside. Light can, however, propagate inside the material within a narrow range of angles.
Xu and Lezec used thin-film deposition techniques at the NIST NanoFab user facility to build a hyperbolic metamaterial block.Guided by computer simulations, they fabricated the block out of 20 extremely thin alternating layers of silicon dioxide glass and silver. To coax external light into the layered material, the researchers added to the block a set of chromium grates with narrow, sub-wavelength spacings chosen to bend incoming red or green  just enough to propagate inside the block. On the other side of the block, the researchers added another set of grates to kick light back out of the structure, although angled away from its original direction.
While the second set of grates let light escape the material, their spacing was slightly different from that of the first grates. As a result, the reverse-direction grates bent incoming light either too much or not enough to propagate inside the silver-glass layers. Testing their structures, the researchers found that around 30 times more light passed through in the forward direction than in reverse, a contrast larger than any other achieved thus far with visible light.
Combining materials that could be made using existing methods was the key to achieving one-way transmission of , Lezec says. Without the intervening silver-and-glass blocks, the grates would have needed to be fabricated and aligned more precisely than is possible with current techniques. "This three-step process actually relaxes the fabrication constraints," Lezec says.
In the future, the new structure could be integrated into photonic chips that process information with light instead of electricity. Lezec thinks the device also could be used to detect tiny particles for biosensing applications. Like the chrome grates, nanoscale particles also can deflect light to angles steep enough to travel through the hyperbolic material and come out the other side, where the light would be collected by a detector. Xu has run simulations suggesting such a scheme could provide high-contrast particle detection and is hoping to test the idea soon. "I think it's a cool device where you would be able to sense the presence of a very small particle on the surface through a dramatic change in light transmission," says Lezec.

Comments

Popular posts from this blog

20,000 megawatts under the sea: Oceanic steam engines

Jules Verne mused about getting energy from heat in the ocean  (Image: Marc Pagani/Getty) Jules Verne imagined this limitless power source in Victorian times – now 21st-century engineers say heat trapped in the oceans could provide electricity for the world IF ANY energy source is worthy of the name "steampunk", it is surely ocean thermal energy conversion. Victorian-era science fiction? Check: Jules Verne mused about its potential in  Twenty Thousand Leagues Under the Sea  in 1870. Mechanical, vaguely 19th-century technology? Check. Compelling candidate for renewable energy in a post-apocalyptic future? Tick that box as well. Claims for it have certainly been grandiose. In theory, ocean thermal energy conversion (OTEC) could provide  4000 times the world's energy needs in any given year , with neither pollution nor greenhouse gases to show for it. In the real world, however, it has long been written off as impractical. This year, a surprising number of pro...

Where the Swastika Was Found 12,000 Years Before Hitler Made Us Uncomfortable About I

Minoan pottery from Crete. The Minoan civilization flourished from 3,000 to 1,100 B.C. (Agon S. Buchholz/Wikimedia Commons) ) Swastika from a 2nd century A.D. Roman mosaic. (Maciej Szczepańczyk/Wikimedia Commons A srivatsa (swastika) sign at Nata-dera Temple, Japan. (Cindy Drukier/Epoch Times) From the Sican/Lambayeque civilization in Peru, which flourished 750 to 1375 A.D. (Wikimedia Commons) Ancient Macedonian helmet with swastika marks, 350-325 B.C., found at Herculanum. (Cabinet des Medailles, Paris/Wikimedia Commons) A Buddha statue on Lantau Island, Hong Kong with a swastika symbol on the chest. (Shutterstock*) A 3,000-year-old necklace found in the Rasht Province of Iran. (Wikimedia Commons) The aviator Matilde Moisant(1878-1964) wearing a swastika medallion in 1912; the symbol was popular as a good luck charm with early aviators. (Wikimedia Commons) A mandala-like swastika, composed of Hebrew letters and surrounded by a circle and a mystica...

There’s a Previously Undiscovered Organ in Your Body, And It Could Explain How Cancer Spreads

Ever heard of the interstitium? No? That’s OK, you’re not alone  —  scientists hadn’t either. Until recently. And, hey, guess what  —  you’ve got one! The interstitium is your newest organ. Scientists identified it for the first time because they are better able to observe living tissues at a microscopic scale, according to a recent study published  in  Scientific Reports , Scientists had long believed that connective tissue surrounding our organs was a thick, compact layer. That’s what they saw when they looked at it in the lab, outside the body, at least. But in a routine endoscopy (exploration of the gastrointestinal tract), a micro camera revealed something unexpected: When observed in a living body, the connective tissue turned out to be “an open, fluid-filled space supported by a lattice made of thick collagen bundles,” pathologist and study author Neil Theise  told  Research Gate . This network of channels is present throughout ...