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NU Physicists Become First To Demonstrate Flat Lens Imaging

Negative refarcation can be exploted to make novel lenses having flat surfaces. All conventional lenses have curved surfaces due to positive index of refraction. However, negative index of refraction allows a flat slab of a material to behave as a lens and focus electromagnetic waves as well as produce a real 3-D image. We have demonstrated this unique feature of imaging by a flat lens, using the phenomenon of all-angle negative refraction in a photonic crystalline material. Conventional optical systems have a single optical axis, limited aperture and cannot focus light onto an area smaller than a square wavelength. In contrast the present flat lens does not have a unique optical axis and is not restricted by the aperture size. We have demonstrated both these features by moving the object by 4 cm: the image moves by a corresponding amount in the same direction (see Figure on right) Note that for the sub-wavelength source we have observed an image of similar size. The unique properties of the flat lens lead to entirely new perspectives on imaging and potentially new applications. A particular advantage of the photonic crystalline material is its scalability to sub-micron dimensions ensuring several possible applications from microwave to optical frequencies. More about Flat Lens
Boston - Dec 02, 2003
Researchers at Northeastern University today announced that they have been able to demonstrate the unique feature of imaging through a flat lens. Using the phenomenon of negative refraction through a novel photonic crystal, Northeastern physicists observed that a flat slab of such material behaves as a lens and focuses electromagnetic waves at microwave frequencies to produce a real image.

The research, published in tomorrow's edition of the journal Nature, represents an important advance in the field of imaging. The lead author on the article, "Imaging by Flat Lens Using Negative Refraction," is Srinivas Sridhar, Ph.D., from the department of physics and the Electronic Materials Institute at Northeastern. Contributors also include NU researchers Patanjali Parimi, Ph.D., Wentao Lu, Ph.D., and Plarenta Vodo.

"The significance of this research is that, for the first time, we have been able to image using a flat surface by employing a special material fabricated from a photonic crystal, which possesses a negative index of refraction," said Sridhar.

"Conventional materials, like glass or Teflon, possess positive indices of refraction and, in order to focus light or microwaves with them, you need to have a curved surface. When the concept of negative refraction emerged about 30 years ago, its most striking proposal was the notion that you could form an image using flat rather than curved surfaces.

"This research not only demonstrated this to be true but is a significant achievement toward the realization of several applications in imaging such as the concept of a ‘superlens' with vastly improved power of resolution."

In the study, the researchers sought to expand upon a recent observation that in certain composite metamaterials, electromagnetic waves bend negatively. The key advance of the new research lies in the design of a new photonic crystal which is an artificial structure usually made out of dielectric or metal designed to control photons in a manner similar to the way a solid crystal controls electrons.

Using a photonic crystal with suitable dispersion characteristics, in this case, an array of alumina rods, the researchers were able to achieve negative refraction at microwave frequencies.

This ability to demonstrate negative bending is significant because it allows considerable control over electromagnetic wave propagation, which could lead to new approaches to a variety of applications from microwave and optical frequencies.

Some of the immediate applications of these negative index materials (also known as left-handed materials) are: sub-wavelength imaging by flat lenses, scanning photon tunneling microscopy, ultra high sensitive phase shifters, leaky wave antennas and optical switches based on negative refraction. Negative index materials could eventually be used to build new components for optical and microwave telecommunications equipment.

"The advantages of focusing by flat lenses are many," said Sridhar. "Conventional optical systems have a single optical axis and limited aperture, both due to curved surfaces, and cannot focus light onto an area smaller than a square wavelength.

"In contrast, the present flat lens does not have a unique optical axis and is not restricted by the aperture size. One of the challenges of this knowledge will be trying to apply it to optical frequencies, which will require fabricating material using nanotechnology. We could potentially see a more immediate impact in the development of microwave antennas and other communications devices."

Related Links
Left-handed Metamaterials
Sagar Lab at Northeastern University
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New USC Process Offers Faster, Cheaper 3D Printouts
Los Angeles - Nov 25, 2003
A University of Southern California inventor has created a machine that can produce 3-dimensional "printouts" in plastic and even metal more quickly and cheaply than widely-used existing systems.


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