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.
Bending light: A new type of material causes light waves (represented by ovals) to move in a way that’s completely different from the way they move in ordinary materials. Credit: Anthony Hoffman, Princeton University
The materials developed at Princeton retain the property of negative refraction, yet they’re much easier to make. Rather than requiring intricate structures, such as the split rings used in the microwave cloaking device, the materials can be made simply by stacking up extremely thin layers of semiconductor material. What’s more, that stacking can be done by the same tools now used to make semiconductor materials for lasers used in telecommunications, says Claire Gmachl, the Princeton researcher who led the work. The new materials consist of alternating layers of indium gallium arsenide and aluminum indium arsenide, and they’re tuned to work in the infrared region of the spectrum.
The first application the Princeton researchers are developing is a flat lens for chemical-sensing devices, an application for which materials that work with infrared light are particularly well suited. Gmachl says that the current optical setups for such devices are bulky because they use conventional lenses. “The first application would be using that material to miniaturize optical setups” by replacing curved lenses with flat ones, she says.
Another early application could be in night-vision devices, which also work with infrared wavelengths. “For people who want to improve night-vision devices, this could be quite interesting,” Smolyaninov says.
This material may contribute to significant advances in many areas, including high-speed communications, medical diagnostics and detection of terrorist threats.
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.
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.