New Lens: GRIN on Steroids
DURHAM, N.C., Dec. 21, 2009 -- Engineers have created a new generation of lens that could greatly improve the capabilities of telecommunications or radar systems to provide a wide field of view and greater detail.
But the lens they fashioned doesn't look anything like a lens. While traditional lenses are made of clear substances – like glass or plastic – with highly polished surfaces, the new lens looks more like a miniature set of tan Venetian blinds. Yet its ability to focus the direction of electromagnetic rays passing through it dramatically surpasses that of a conventional lens, the engineers say.
The latest advance was made possible by the ability to fabricate exotic composite materials known as metamaterials. The metamaterial in these experiments is not so much a single substance, but the entire man-made structure which can be engineered to exhibit properties not readily found in nature.
A close-up view of the new lens. While traditional lenses are made of clear substances with highly polished surfaces, the new lens looks more like a miniature set of tan Venetian blinds. (Photos: Duke University Photography)
The prototype lens, which measures 4 in. by 5 in. and less than an inch high, is made up of more than 1000 individual pieces of the same fiberglass material used in circuit boards and is etched with copper. It is the precise arrangement of these pieces in parallel rows, that directs the rays as they pass through.
"For hundreds of years, lens makers have ground the surfaces of a uniform material in such a way as to sculpt the rays as they pass through the surfaces," said Nathan Kundtz, post-doctoral associate in electrical and computer engineering at Duke University's Pratt School of Engineering. "While these lenses can focus rays extremely efficiently, they have limitations based on what happens to the rays as they pass through the volume of the lens.
"Instead of using the surfaces of the lens to control rays, we studied altering the material between the surfaces," Kundtz said. "If you can control the volume, or bulk, of the lens, you gain much more freedom and control to design a lens to meet specific needs."
The results of his experiments, which were conducted in the laboratory of senior researcher David R. Smith, the William Bevan Professor of Electrical and Computer Engineering, appeared as an advanced online publication of the journal Nature Materials. This is the first demonstration of what was thought to be theoretically possible.
Recognizing the limitations of traditional lenses, scientists have long been investigating other options, including those known as gradient index (GRIN) lenses. These are typically clear spheres, and while they have advantages over traditional lenses, they are difficult to fabricate and the focus point is spherical. Additionally, because most sensing systems are oriented in two dimensions, the spherical image doesn't always translate clearly on a flat surface.
The new lens, however, has a wide angle of view, almost 180°, and because its focal point is flat, it can be used with standard imaging technologies. The latest experiments were conducted with microwaves, and the researchers say it is theoretically possible to design lenses for wider frequencies.
Duke University's David Smith (left) and Nathan Kundtz, about to test the new lens.
"We've come up with what is in essence GRIN on steroids," said Smith, whose team used similar metamaterials to create one of the first "cloaking" devices in 2006. "This first in a new class of lenses offers tantalizing possibilities and opens a whole new application for metamaterials.
"While these experiments were conducted in two dimensions, the design should provide a good initial step in developing a three-dimensional lens," Smith said. "The properties of the metamaterials we used should also make it possible to use infrared and optical frequencies."
The researchers say a single metamaterial lens could replace traditional optical systems requiring vast arrays of lenses and provide clearer images. They could also be used in large-scale systems such as radar arrays to better direct beams, a task not possible for traditional lenses, which would need to be too large to be practical.
The research was supported by the Army Research Office's Multiple University Research Initiative (MURI).
For more information, visit: www.duke.edu
- focal point
- That point on the optical axis of a lens, to which an incident bundle of parallel light rays will converge.
- A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.
- An electromagnetic wave lying within the region of the frequency spectrum that is between about 1000 MHz (1 GHz) and 100,000 MHz (100 GHz). This is equivalent to the wavelength spectrum that is between one millimeter and one meter, and is also referred to as the infrared and short wave spectrum.
- Pertaining to optics and the phenomena of light.
- The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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