Shape shifting: Light is confined to different parts of the waveguide when the diameter or height of the nanowire changes. From left to right: light travels inside a 400-nanometer nanowire placed 100 nanometers above the surface; some light begins to travel between the nanowire and the surface when the diameter is reduced to 200 nanometers; when the nanowire is just two nanometers above the surface, light is trapped in the tiny gap for both 200-nanometer and 400-nanometer nanowires.
“This could truly enable a revolution in the [nanophotonics] field,” says Marin Soljacic, a physics professor at MIT. For example, the resolutions of sensing and imaging techniques are limited by the wavelength of light they use to measure objects; anything beneath the resolution can’t be seen. A device that confines light beyond its natural wavelength, however, could measure and return information about what lies beyond these limits.
The group is cautiously optimistic about its innovation. “This is probably our biggest breakthrough in the last seven or eight years,” says Xiang Zhang, a professor of mechanical engineering at UC Berkeley, who led the research. “But we still have a long way to go.” The researchers have already started to demonstrate in experimental devices the performance that their simulations predicted. However, they have only tested the devices with visible light frequencies, which are still hundreds of nanometers smaller than the infrared frequencies used in communications. And while a propagation distance of 150 microns is good, says Zhang, they want a distance of at least a millimeter for practical devices on integrated chips.
With continued refinement, the technique could play several roles in optical computing. The setup could be used to steer light through certain paths on chips. The group is even toying with the idea of using the device to produce an ultrasmall light source. Still, any practical devices are several years away. “They will have to master the fabrication,” says Soljacic. “But the simulations seem convincing, and I have complete faith that it will work.”