Metamaterials that exhibit negative indices of refraction have made headlines recently with their promise of “invisibility cloaks” that bend light round an object. Hopes were probably higher than what is realistic, however, because the candidate materials had the desired response over only narrow wavelength bands and were generally “2D”, so were suited only to making cylindrical cloaks.

Now Jason Valentine of the University of California in Berkeley and colleagues have reported a true 3D optical negative-index metamaterial based on a fishnet structure of metals and dielectrics. They measured the refractive index by creating a prism from the structure and observing the angle of refraction of light passing through it – the classic measurement using Snell’s law. The alternating layers of silver and magnesium fluoride turn out to have a negative index over a broad range of the optical electromagnetic spectrum, from 1200–1800 nm.

Further reading

J Valentine et al. 2008 Nature 455 376.