Nanoantennas Can Change Phase of Light
Researchers at Purdue University found that arrays of plasmonic nanoantennas can be used to manipulate the phase, a wave shape, of light as it propagates.
The scientists now believe that they have found a path that could enable more powerful microscopes, telecommunications and computers. Specifically, the discovery is expected to have effects on technologies for "steering and shaping laser beams for military and communications applications, nanocircuits for computers that use light to process information, and new types of powerful lenses for microscopes."
The research builds on a previous modification how scientists have described how light reflects and refracts or bends while passing from one material into another, which is referred to as Snell's law. Each material has its own refraction index and all natural materials show positive refraction indexes. However, Purdue's nanoantennas can change the refraction and even achieve negative angles.
"Importantly, such dramatic deviation from the conventional Snell's law governing reflection and refraction occurs when light passes through structures that are actually much thinner than the width of the light's wavelengths, which is not possible using natural materials," said Vladimir Shalaev, scientific director of nanophotonics at Purdue's Birck Nanotechnology Center. "Also, not only the bending effect, refraction, but also the reflection of light can be dramatically modified by the antenna arrays on the interface, as the experiments showed."
According to the scientists, the nanoantennas feature V-shaped structures that are made of gold and are placed on top of a silicon layer. The antennas are 40 nm wide. Shalaev said that they are able to transmit light through an ultrathin "plasmonic nanoantenna layer" that is about 50 times smaller than the wavelength of light it is transmitting. "This ultrathin layer of plasmonic nanoantennas makes the phase of light change strongly and abruptly, causing light to change its propagation direction, as required by the momentum conservation for light passing through the interface between materials," Shalaev said.