Metamaterial Offers Simpler Route to Slow Light

Manipulating the speed of light more effectively than cold-atom methods, a metamaterial design could find use in optical networks and sensors.

The "slow light" effect was demonstrated using terahertz waves but could be applied to other wavelengths including visible light, according to researchers at The University of Alabama.

"Slow light will lead to the development of optical buffers and delay lines as essential elements of future ultrafast all-optical communication networks that could meet the ever-increasing demands for long-distance communications," said professor Seongsin Margaret Kim.

From left, graduate student Mohammad Parvinnezhad Hokmabadi, Dr. Patrick Kung and Dr. Seongsin Margaret Kim work with the terahertz metamaterial. Courtesy of the University of Alabama.

"In addition, enhanced interaction of photons with matter by lowering the speed of light gives rise to reduced power consumption in nonlinear optical switching devices and ultra-accurate sensing performance of optical sensors."

Light is generally accepted to travel at a constant speed, but its group velocity can be slowed by passing through refractive materials. Compared to its top speed in a vacuum, light travels slightly slower in air and slightly slower still in water. These changes in speed are fairly insignificant, however.

Metamaterials, on the other hand, can be engineered with nanoscale structures that interact with light to significantly slow or even stop it.

Metamaterials consist of patterns whose size, geometry and orientation can be selected for exotic optical properties. Courtesy of the University of Alabama.

Unlike the best known methods for slowing light, which involve cold atoms, metamaterials use no energy and are much less complex to implement. They also show promise for use in optical filters, modulators, invisibility cloaks, superlenses and light absorbers.

The Alabama researchers fabricated and characterized a thin, flexible metamaterial film on a silicon substrate that behaves as if it is 1000 times thicker than its actual thickness. This "effective thickness" had been difficult to gauge previously, the researchers said.

The work was supported by the National Science Foundation and published in Scientific Reports (doi: 10.1038/srep14373 [open access]).