A new device from Caltech can change the direction and shape of a light beam in just 74 femtoseconds. This is about the same time it takes a light pulse to cross a human hair.
This experimental technology could lead to optical systems that react much faster than current beam-steering equipment. Such fast control is important for cameras, sensors, communication networks, scientific tools, and new types of photonic computing.
How the Silicon Metasurface Works
Most tools that manipulate light cannot keep up with light itself. Mirrors need to move, liquid crystals must rearrange, or electronic signals have to change a material's properties. Even if these processes seem fast, they are slow compared to light's speed.
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Start Your News DetoxResearchers have now shown an ultrathin surface that can steer and reshape light in only 74 femtoseconds. These findings were published in Nature Nanotechnology.
The research was done in Professor Harry Atwater's lab at Caltech. Dr. Claudio Hail, now a professor at the University of California, Berkeley, led the study. Dr. Lior Michaeli, who heads the Meta-Optomechanics Laboratory at Tel Aviv University, was also a co-author.
The device is a metasurface. This is a thin optical layer with patterns smaller than the wavelength of light. Unlike a traditional lens that uses curved glass, a metasurface changes light using tiny, carefully placed features on an almost flat surface.
This metasurface has tiny silicon structures designed to briefly trap and focus light. This design makes the light interact more strongly with the silicon.
A short control pulse changes the silicon's optical properties through something called the optical Kerr effect. With this effect, intense light briefly changes a material's refractive index, which affects how light travels through it.
The Kerr effect can happen in less than a femtosecond, but it's usually too weak to be useful. The researchers solved this by designing a high-quality metasurface that boosts this interaction. This allowed one light pulse to control another without any moving parts or slower changes involving electrical charges.
Programmable Beam Steering and Shaping
Dr. Hail explained that the main idea was to create a metasurface whose optical response isn't fixed. By changing the light pattern, they can reconfigure how the device steers and shapes light very quickly.
In lab tests, the team redirected a light beam by up to 13 degrees in either direction. They could control the direction by changing the pattern of the control pulse.
They also used this method to reshape the outgoing beam and create different light patterns. The surface could be reprogrammed with light, instead of being designed for only one task.
Professor Atwater noted that light usually interacts weakly with matter, making it hard to control one light beam with another. The metasurface improves this interaction, allowing a small and fast material change to create a useful change in the outgoing beam.
Dr. Michaeli found it exciting to see an idea become real. He said the ultrafast effect they wanted to use is naturally very weak. They had to design the metasurface to amplify the effect enough to measure it and use it to steer and shape light.
The observed switching time was close to the length of the laser pulse used. This suggests the metasurface might be able to switch even faster with shorter pulses.
The surface also resets quickly after the control pulse is gone. Because it doesn't use moving parts or long-lasting electrical charges, it can return to its original state almost instantly.
Towards All-Optical Computing and Communications
Today's communication networks use light to move a lot of information. However, this information often needs to be turned into an electrical signal for processing or routing. Then it's converted back into light for sending.
These conversions add complexity, delays, and energy costs. A programmable device that can manipulate light directly could allow some operations to stay entirely optical.
This technology could be used in quickly reconfigurable communication hardware, compact imaging systems, advanced sensors, dynamic holography, and photonic processors. Active metasurfaces are being studied to control properties like a beam's direction, intensity, phase, polarization, and spectrum on a small platform.
Dr. Michaeli added that this work shows a bigger opportunity: using engineered structures to strengthen how light and matter interact. This can turn them into tools for control, sensing, and information processing.
The researchers emphasize that this experiment is a proof of concept. It's not a finished product ready to replace current optical hardware.
However, the study shows that optical components don't have to be the slow part of a light-based system. By using tiny structures to boost a weak physical effect, the researchers showed that one light beam can quickly and programmably control another.
Deep Dive & References
Ultrafast, reconfigurable all-optical beam steering and spatial light modulation - Nature Nanotechnology, 2026
