Plate Nº 47 · recorded October 10, 2026
PhysicsReported finding
Caltech Chip Steers Light in 74 Femtoseconds Using Light Alone
Caltech engineers redirected a light beam in 74 femtoseconds using only light and a nanoscale silicon metasurface, steering angles up to 13 degrees without any electronic signal.
By James Calloway4 min read735 words
In brief
- Caltech researchers steered a light beam in 74 femtoseconds, roughly the time light takes to cross a human hair.
- The device redirected light by angles of up to 13 degrees using a pump beam and a silicon metasurface.
- The findings were published in Nature Nanotechnology on September 18, 2026.
- The speed limit came from the 74-femtosecond laser pulse, not the material, suggesting faster operation is possible.
- The work was led by Harry Atwater with lead author Claudio U. Hail.
A Calteam of Caltech engineers has redirected a beam of light in just 74 femtoseconds — 74 quadrillionths of a second, roughly the time light takes to cross the width of a human hair — using nothing but another beam of light and a nanoscale silicon sheet. The team, led by Harry Atwater, published its results in Nature Nanotechnology on September 18, 2026.
The device steered light by angles of up to 13 degrees. And the researchers say the current speed limit comes from their laser pulses, not from the material itself, which means even faster control may be within reach.
Why is steering light so hard?
Photonic technologies promise faster communications, more powerful computing, and highly sensitive sensors, because light carries huge amounts of information at extraordinary speed. But these systems only work if researchers can precisely and rapidly control where light goes.
Existing light-steering technologies — from liquid-crystal projector panels to optical chips in telecom systems — depend on changing the electronic properties of a material. Electrons get pushed into higher energy states, then fall back and release their excess energy. That relaxation step takes time, which bottlenecks most devices at nanosecond or picosecond timescales.
Atwater's team removed the electrical signal entirely. Instead, a powerful beam of light, called the pump, carried a carefully designed pattern that temporarily altered a material's optical behavior. A weaker beam, the probe, passed through the same material and changed direction according to that pattern.
"Steering light with light is very challenging because light typically interacts very weakly with matter," Atwater, the Howard Hughes Professor of Applied Physics and Materials Science at Caltech, said in a statement. "Using optical metasurfaces — ultrathin, carefully nanoengineered sheets — we can up the interaction strength to make this possible with much higher efficiency."
What makes it fast?
The system exploits the optical Kerr effect. When an intense beam passes through a material, it briefly produces a very small change in the material's refractive index — the quantity that describes how much light slows down and bends inside it.
The effect stems from changes in how electrons move within their orbitals, the regions around an atom's nucleus where electrons are most likely to be found. Crucially, the electrons never enter separate, longer-lasting excited states. The change appears and vanishes almost as fast as the light pulse itself, so there is no waiting for electrons to relax.
There was a catch, though. On its own, the optical Kerr effect is far too weak to redirect a beam by any practically useful amount.
How did the researchers amplify the effect?
To strengthen the response, the team built a metasurface — an ultrathin, nanoengineered sheet — from a film of amorphous silicon covered with nanoscale pillars, each smaller than the wavelength of the pump light.
By tuning the pillars' size and spacing, the researchers made light linger inside the metasurface and circulate within it rather than passing straight through. That extra interaction time amplified the tiny refractive-index change in the silicon until it was strong enough to steer the probe beam.
The measured modulation speed — 74 femtoseconds — matched the duration of the pump pulse, which was also 74 femtoseconds. The researchers say the metasurface's fundamental properties do not set the speed limit; the laser does.
That leaves room to go faster. With further development, the technology could reach timescales relevant to emerging photonic concepts such as time crystals and synthetic time-varying optical materials.
Who did the work?
Lead author Claudio Hail carried out the research as a postdoctoral scholar in Atwater's Caltech lab and is now an assistant professor of mechanical engineering at UC Berkeley. Lior Michaeli, the third author, completed the work as a postdoctoral scholar at Caltech and is now an assistant professor of electrical and computer engineering at Tel Aviv University.
The paper, titled "Ultrafast, reconfigurable all-optical beam steering and spatial light modulation," appears in Nature Nanotechnology (2026, vol. 21, issue 7, p. 940).
Funding came from the Air Force Office of Scientific Research and its Meta-Imaging Multidisciplinary University Research Initiative, the Swiss National Science Foundation, the Fulbright Fellowship program, and the Breakthrough Foundation. The Kavli Nanoscience Institute at Caltech provided infrastructure and support.
As with any laboratory demonstration, practical applications in communications, computing, and sensing will require further engineering. But the result shows that light can now steer light on timescales that electronics-driven devices cannot approach.
via dx.doi.org (Original)
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