First Negative-Index Refraction in the Near-Infrared

One of the hottest subjects in optical science right now is the study of materials -- sometimes "meta-materials" consisting of arrays of tiny metal rings and rods -- characterized by a negative index of refraction. First in the microwave portion of the electromagnetic spectrum, and later at shorter wavelengths, negative-index research has sought to characterize and exploit a process in which a light beam, passing from air into the special medium, refracts not toward but away from the perpendicular to the medium's surface.

Such negative-index materials (NIMs) might lead to novel lensing, antennas, waveguides, and filtering applications. NIMs operating in the optical range promise to create entirely new prospects for controlling and manipulating light, optical sensing, and nanoscale imaging and photolithography, and thus enable entirely new device applications.

A Purdue group observes negative-index behavior all the way into the near-infrared spectral region, around a wavelength of 1.5 microns, exactly where fiber-optic telecommunications is carried out. Vladimir Shalaev and his colleagues achieve negative refraction in a material consisting of tiny gold rods residing in a dielectric matrix.

The material, with a refractive index of -0.3, was too "lossy" (too much of the light was absorbed) to exhibit "perfect lensing," a type of refraction in which a cone of light falling on a flat-panel sample of negative-index material could be focused to a point. However, Shalaev (shalaev@ecn.purdue.edu, 765-494-9855) believes this problem can be overcome. Furthermore, he is confident his lab will be able to extend his negative-index results into the visible-light part of the spectrum.

Shalaev et al., Optics Letters, 15 December 2005