Microwave focusing

Researchers at

today announced that they have been able to demonstrate focusing of a plane microwave by a plano-concave lens fabricated from a photonic crystal (PhC) specially designed to have negative refractive index and left-handed electro-magnetic properties.

The Northeastern researchers also performed an inverse experiment in which a plane wave is produced from a source placed at the focal point of the lens.

The research, supported by the US National Science Foundation and the Air Force Research Laboratories, represents an important advance in the field of imaging and will be published in the May 16th edition of Applied Physics Letters.

The authors of the article “Focusing by Plano-Concave Lens Using Negative Refraction” are Plarenta Vodo, Patanjali Parimi, PhD, Wentao Lu, PhD, and Srinivas Sridhar, PhD, from the department of physics and the Electronic Materials Research Institute at Northeastern University.

“Negative refraction in left-handed materials has triggered intense interest in designing novel microwave and optical elements. In 2003, we demonstrated imaging by a flat lens for the first time,” said Sridhar.

“However, the flat lens operates only when the source is close to the lens. For the majority of applications of lenses in optics, astronomical telescopes, commercial and defence microwave communications, far field imaging is required. Negative refraction allows focusing of a far field radiation by concave rather than convex surfaces, with the advantage of reduced aberration or distortion. Lenses with reduced aberration produce sharper images with enhanced resolution.”

In the study, the researchers demonstrate that a real image of a far field radiation microwave source can be produced using a left-handed PhC lens. They also report on an inverse experiment in which the lens produces plane waves from a point source placed at the focal length. The results of the experiments confirm that far field focusing is realizable and open the door for several applications of left-handed materials.

Other advantages of the plano-concave PhC lens include its light weight, making it suitable for space applications, and the tailor-made refractive index achievable in PhC materials, allowing for further control of the focal length and helping to reduce the length of optical systems.