Lens Once Deemed Impossible Now Rules the Waves

For centuries, microscopes, eyeglasses, and magnifying glasses have slammed into a built-in limitation: No matter how good their lenses, the laws of optics dictate that details smaller than a wavelength of light are irretrievably lost. Undaunted, physicists have built a radically different breed of lens with the potential for perfect resolution. “It smashed the barrier; it crashed through the glass ceiling,” says John Pendry, a physicist at Imperial College London.

The new lens, which George Eleftheriades and Anthony Grbic of the University of Toronto describe in an upcoming issue of Physical Review Letters, focuses microwaves—long-wavelength radiation that falls next to radio waves in the electromagnetic spectrum. By etching a flat plane of plastic with a wire grid studded with capacitors and inductors, the researchers created a material with a negative refractive index—one that bends waves in the opposite direction from normal materials. Because of transmission losses, lenses made from normal materials cannot distinguish objects less than half a wavelength apart, but “left-handed” (negative-index) materials can. The new lens, for example, resolves objects just one-sixth of a microwave wavelength apart.

The left-handed lens achieves super-resolution by resurrecting waves that carry the subwavelength details of an object. Such so-called evanescent waves usually fizzle to nothing before they pass through a conventional lens. But the Toronto group's lens traps them like surf sloshing between two piers and amplifies them enough to reach the focal point (see diagram).

The super-resolving lens is a significant proof of principle, Pendry says. In 2000, Pendry predicted that left-handed materials would make possible marvels such as completely flat lenses with perfect resolution and zero loss (Science, 10 November 2000, p. 1066). Some physicists thought such materials were physically impossible, but researchers soon created them and began working on left-handed lenses (Science, 19 December 2003, p. 2043). In February, physicists at the Institute for Theoretical and Applied Electromagnetics in Moscow announced a super-resolving lens, but their technique required the object to be almost touching the lens, making it impractical for real-life applications. The new lens overcomes that limitation.

Eleftheriades dreams of applying the left-handed lens to medical imaging. “If you were to scale down to the frequencies of an MRI (20 megahertz), you could place the human body 1 meter away and still get super-resolution,” he says—a vast improvement over current instruments.