Telecommunications

Manipulating light at will - Duke metamaterials strike again

A fundamental property of metamaterials is the ability to produce negative refraction
A fundamental property of metamaterials is the ability to produce negative refraction
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A surface metamaterial (Image: University of Essex)
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A surface metamaterial (Image: University of Essex)
A metamaterial form to induce total absorption of light (Image: Duke University)
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A metamaterial form to induce total absorption of light (Image: Duke University)
A scanning electron microscopy (SEM) image of the frequency-tunable planar metamaterial. An individual unit cell (Image: Nature Photonics)
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A scanning electron microscopy (SEM) image of the frequency-tunable planar metamaterial. An individual unit cell (Image: Nature Photonics)
A scanning electron microscopy (SEM) images of the frequency-tunable planar metamaterial. A periodically patterned square array. (Image: Nature Photonics)
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A scanning electron microscopy (SEM) images of the frequency-tunable planar metamaterial. A periodically patterned square array. (Image: Nature Photonics)
The metamateral developed by Duke engineers (Image: Duke University)
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The metamateral developed by Duke engineers (Image: Duke University)
A fundamental property of metamaterials is the ability to produce negative refraction
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A fundamental property of metamaterials is the ability to produce negative refraction
A scanning electron microscope image of the fabricated structure, developed by UC Berkeley researchers. The alternating layers form small circuits that can bend light backwards. (Image: Jason Valentine/UC Berkeley)
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A scanning electron microscope image of the fabricated structure, developed by UC Berkeley researchers. The alternating layers form small circuits that can bend light backwards. (Image: Jason Valentine/UC Berkeley)
The micro are mighty. An array of micron-sized circuits twist in unison to form a metamaterial terahertz lens. (Image: H. Tao et al./ Boston University)
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The micro are mighty. An array of micron-sized circuits twist in unison to form a metamaterial terahertz lens. (Image: H. Tao et al./ Boston University)
A schematic of the first 3-D "fishnet" metamaterial that can achieve a negative index of refraction at optical frequencies. The alternating layers form small circuits that can bend light backwards. (Image: Jason Valentine/UC Berkeley)
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A schematic of the first 3-D "fishnet" metamaterial that can achieve a negative index of refraction at optical frequencies. The alternating layers form small circuits that can bend light backwards. (Image: Jason Valentine/UC Berkeley)
An optical metamaterial consisting of split rings of gold in a polymer matrix. Electron micrograph (Image: University of Stuttgart)
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An optical metamaterial consisting of split rings of gold in a polymer matrix. Electron micrograph (Image: University of Stuttgart)
Duke University engineers with the new metamaterial (Image: Duke University)
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Duke University engineers with the new metamaterial (Image: Duke University)
Left-handed metamaterial flat lens consisting of an array of 3 by 20 by 20 unit cells. With a unit cell width of 5 mm, this geometry shows reversed refraction and left-handed focusing properties at microwave frequencies between 10 and 11 GHz. (Image: NASA)
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Left-handed metamaterial flat lens consisting of an array of 3 by 20 by 20 unit cells. With a unit cell width of 5 mm, this geometry shows reversed refraction and left-handed focusing properties at microwave frequencies between 10 and 11 GHz. (Image: NASA)

Duke University is on a roll, showing off yet another potentially game-changing property of the exotic man-made substances known as metamaterials. This time the property could have deep consequences for the transmission of information via light. Maybe the most important potential use of all.

Duke University's Pratt School of Engineering is building an enviable reputation for the proof and demonstration of potential metamaterial properties. We have written before about Duke's proof-of-concept demonstrations with the 'invisibility cloak' and the possibility of boosting wireless power transmission.

The Holy Grail of photonic research, however, is the creation of an optical switcher that would allow connection of multiple fiber-optic data streams without conversion to electronic signals - transmission speed would increase by orders of magnitude and energy usage would decrease dramatically, an important consideration when at least 10 percent of the energy consumption of the U.S. is due to computation and data access. The engineers at Duke say they have developed a metamaterial that allows them to manipulate the frequency and direction of light at will.

Duke University engineers with the new metamaterial (Image: Duke University)
Duke University engineers with the new metamaterial (Image: Duke University)

Some naturally-occurring crystals can take the light from a laser, double its frequency and focus it into a beam. This phenomenon is used for solid state laser pointers, for example. What Duke graduate students Alec Rose and Da Huang have achieved is to introduce similar non-linearities in a controllable way, allowing them to steer the direction of the frequency-doubled (second harmonic) beam. This has enormous implications for optical switching.

Metamaterials are human-engineered lattice structures of different materials that could not occur in nature and which can produce negative refraction as light passes through them. To work on light beams these structures have to be built at the nano scale and this can be somewhat inconvenient for research purposes. At Duke the engineers use longer wavelength microwaves to test materials that can be constructed at the human scale for proof-of-concept.

The metamateral developed by Duke engineers (Image: Duke University)
The metamateral developed by Duke engineers (Image: Duke University)

The device itself, which measures six inches by eight inches and about an inch high (15 x 20 x 2.5 cm), is made up of row upon row of individual pieces arranged in parallel rows. Each piece is made of the same fiberglass material used in circuit boards and is etched with copper circles. Each copper circle has a tiny gap that is spanned by a diode, which when excited by microwave radiation passing through it, breaks its natural symmetry, creating non-linearity.

"The trend in telecommunications is definitely optical," Rose said. "To be able to control light in the same manner that electronics control currents will be an important step in transforming telecommunications technologies."

It's now for others to take the proven metamaterial design down to the nanometer scale for testing with visible light. Check out the gallery for other metamaterial forms.

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