Photonic Crystal Planoconcave Lenses Focus Microwaves

A team at Northeastern University in Boston has reported the successful fabrication of photonic crystal planoconcave lenses with refractive indices ranging from −0.3 to −1.2, enabling them to focus far-field microwave radiation. The work, which is described in the May 16 issue of Applied Physics Letters, confirms theoretical predictions of the behavior of such "left-handed materials" and has potential in the development of novel lenses for space, telecommunications and imaging applications.

Building on previous research that resulted in the demonstration of imaging using a flat photonic crystal (see Photonics Spectra, January 2004, page 27), the scientists designed three planoconvex lenses -- comprising 2-D periodic arrays of alumina rods -- with radii of curvature of 13.5, 17.5 and 22 cm. Transmission intensity maps of 7.8- to 9.5-GHz microwaves revealed that incoming plane waves were focused to a point centimeters from the surface of the lens. Inverse experiments confirmed that microwaves emitted from a point source at the foci of the lenses emerged from the flat face as a plane wave.

The left-handed lenses have potential advantages over their positive-refractive-index planoconvex counterparts, the scientists note. For one, they promise to display lower geometrical aberration for lenses of the same radius of curvature. For another, they weigh much less than a conventional lens of the same focal length, making them particularly attractive for space applications.