Caltech Team Steers a Beam of Light Using Only Another Beam of Light

Researchers at the California Institute of Technology (Caltech) have devised a way to steer a beam of light almost instantly, using only another beam of light to do the steering. In a paper published in the journal Nature Nanotechnology, the team changed the direction of a light beam in just 74 femtoseconds — 74 quadrillionths of a second.

Earlier light-steering methods worked by altering the electronic properties of optical chips or liquid crystal panels, exciting electrons to bend the path of light. Those approaches topped out at nanosecond or, at best, picosecond speeds — billionths or trillionths of a second — thousands of times slower than the new technique.

The team, led by Claudio Hall, a former Caltech postdoctoral scholar now an assistant professor at the University of California, Berkeley, and Harry Atwater, Howard Hughes Professor of Applied Physics and Materials Science at Caltech, instead used the optical Kerr effect, in which an intense beam of light briefly changes a material's refractive index, the property that governs how much light bends when passing through it. By shining a strong "pump" beam calibrated to the material and then sending a weaker "probe" beam through it, the researchers deflected the probe beam by up to 13 degrees. "Steering light with light is very challenging," Atwater said, "because light typically interacts very weakly with matter."

To strengthen that interaction, the team coated a sheet of nanoscale pillars, spaced closer together than the pump beam's wavelength, with amorphous silicon, which slowed and recirculated the light as it passed through. The researchers say the modulation speed could be pushed even faster with further refinement of this nanostructured surface.