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Researchers Build Optical Nanostructures To Enable Self-Focusing Light

by Editor1 last modified July 20, 2011 - 15:14

An international team led by Columbia University’s Fu Foundation School of Engineering and Applied Science has built optical nanostructures that can control light dispersion and engineer the index of refraction. This control of light propagation via photonic chips could prove a major breakthrough for telecommunications.

Researchers Build Optical Nanostructures To Enable Self-Focusing Light

Nanofabricated superlattices consist of alternating stacks of negative index photonic crystals and positive index homogeneous dielectric media.

This work represents the first time simultaneous phase and zero-index observations have been made on the chip-scale and at the infrared wavelength.

It also demonstrates it is possible for light (or any electromagnetic waves) to propagate from Point A to Point B without accumulating any phase, spreading through the artificial medium as if the medium is completely missing in space, according to Chee Wei Wong, associate professor of mechanical engineering at Columbia Engineering, who co-led the team.

"This [work] can enable self-focusing light beams, highly directive antennas, and even potentially an approach to cloak or hide objects, at least in the small-scale or a narrow band of frequencies currently," ong added.

Serdar Kocaman, an electrical engineering PhD candidate at Columbia Engineering, is another co-leader.

"We're very excited about this. We've engineered and observed a metamaterial with zero refractive index," said Kocaman. "What we've seen is that the light disperses through the material as if the entire space is missing. The oscillatory phase of the electromagnetic wave doesn't even advance such as in a vacuum — this is what we term a zero-phase delay."

Then two worked in collaboration with scientists at the University College of London, Brookhaven National Laboratory, and the Institute of Microelectronics of Singapore.

This exact control of optical phase is based on a unique combination of negative and positive refractive indices. All natural known materials have a positive refractive index.

By sculpturing artificial subwavelength nanostructures, the team found they could control the light dispersion so that a negative refractive index appeared in the medium. Then, they cascaded the negative index medium with a positive refractive index medium so that the complete nanostructure behaved as one with an index of refraction of zero.

"Phase control of photons is…a big step forward in figuring out how to carry information on photonic chips without losing control of the phase of the light," Wong added.

The study appeared on Nature Photonics website July 10.