Light travels at 300,000 kilometers per second, and until now, nobody had found a practical way to steer it without slowing it down first. Caltech researchers just did it in 74 femtoseconds — roughly the time it takes light to cross the width of a human hair.

  • 74 femtoseconds to redirect the beam — the new speed record
  • 13 degrees the steering angle achieved in testing
  • 300,000 km/s the speed of the light being controlled
  • 1 ultrathin silicon metasurface, covered in pillars smaller than a wavelength of light

Steering Light With Light

Every optical chip and display made today, from LCD screens to fiber-optic routers, steers light using electronics. Electrons get excited into a higher energy state, then fall back down, and that fall takes time — anywhere from nanoseconds to picoseconds. That delay has been a hard ceiling on how fast optical systems can respond.

The Caltech team, led by physicist Harry Atwater and postdoctoral researcher Claudio Hail (now at UC Berkeley), skipped the electronics entirely. Instead, they used one pulse of light to redirect a second, weaker beam, relying on something called the optical Kerr effect, where an intense light pulse briefly changes how a material bends light. Because no electrons need to settle back down, the effect appears and disappears as fast as the pulse itself.

"Steering light with light is very challenging because light typically interacts very weakly with matter," Atwater said.

How the Metasurface Works

On its own, the Kerr effect is too weak to be useful for anything. The breakthrough came from amplifying it with a "metasurface" — a film of amorphous silicon coated in nanoscale pillars, each smaller than the wavelength of light passing through it. Those pillars trap light and force it to circulate longer than it normally would, which magnifies the Kerr effect enough to actually bend a second beam.

"Using optical meta-surfaces, we can up the interaction strength to make this possible with much higher efficiency."

In testing, that setup let the team steer a beam by angles of up to 13 degrees, with the modulation speed limited only by the length of the pump laser pulse — meaning even faster steering should be possible with shorter pulses. The findings were published in Nature Nanotechnology, with additional detail from Caltech's official announcement.

Why Speed Matters

Faster beam-steering has direct implications for fiber-optic communication networks, which already carry most of the world's internet traffic as pulses of light. A chip that can redirect those pulses on a femtosecond timescale, without waiting on electronics, could let future networks move more data with less latency.

The same approach could speed up photonic computing, where information is processed using light instead of electrical current, and ultrafast sensing applications in physics and biology that need to catch signals that come and go in a fraction of a nanosecond. For now, the team has proven the concept works. The next step is refining the metasurface design to see just how much further the speed limit can be pushed.