Purdue University engineers have created a material with a negative index of refraction in the wavelength of light, paving the way for better communications and imaging technologies.
The material consists of tiny parallel gold nanorods that conduct clouds of electrons called plasmons with a frequency of light referred to as the near-infrared, at a wavelength of 1.5 mm — the same used in fiber optic communications.
The research was completed by Vladimir Shalaev, the Robert and Anne Burnett Professor of Electrical and Computer Engineering; graduate research assistants Wenshen Cai and Uday K. Chettiar; doctoral student Hsiao-Kuan Yuan; senior research scientists Andrey K. Sarychev and Vladimir P. Drachev; and principal research scientist Alexander V. Kildishev.
The nanorods can reverse refraction, which occurs as electromagnetic waves bend when passing from one material into another and is caused by a change in the speed of light as it passes from one medium into another. Scientists measure this bending of radiation by its index of refraction. All natural materials, such as glass, air, and water, have positive refractive indices.
Harnessing materials with a negative index of refraction may enable taking optical images of objects that are smaller than the wavelength of visible light for research and medical imaging. It could also promote the development of photo-nanolithography to etch smaller electronic devices and circuits for more powerful computers; and new types of antennas, computer components, and consumer electronics that use light to carry signals and process information, thus increasing communication speed.
The electrons move in unison as a single object instead of millions of individuals. Light shined onto them induces an electro-optical current in the circuit. Each rod is about 100 nm wide and 700 nm long.
“These rods conduct current because they are a metal, producing an effect we call optical inductance, while a material between the rods produces another effect called optical capacitance,” Shalaev said. “The result is the formation of a very small electromagnetic circuit, but this circuit works in higher frequencies than normal circuits, in a portion of the spectrum we call optical frequencies, which includes the near-infrared. So we have created a structure that works as kind of an optical circuit and interacts effectively with both field components of light: electrical and magnetic.”
The research was funded by the U.S. Army Research Office and the National Science Foundation and is affiliated with Purdue's Birck Nanotechnology Center.