Researchers at Caltech have demonstrated a device capable of redirecting light beams in remarkably brief timeframes, accomplishing the task in 74 femtoseconds—approximately the duration required for light to traverse the width of a human hair. The work addresses a significant challenge in photonic technology development, where precise and rapid control of light direction is essential for advancing communications systems, computing capabilities, and sensor applications.
Traditional light steering approaches rely on modulating electronic properties of materials, such as those found in liquid-crystal projectors and telecommunications optical chips. These systems typically operate on nanosecond or picosecond timescales because they require electrons to transition to higher energy states and subsequently relax back to lower states, a process that inherently creates timing constraints. The Caltech team circumvented this limitation by employing an entirely optical approach, using an intense light beam with a precisely engineered pattern to temporarily modify the optical characteristics of a material through which a secondary light beam would pass.
The system leverages the optical Kerr effect, a phenomenon whereby an intense light beam produces minute changes in a material’s refractive index—the property governing how much light slows and bends when traveling through that material. Notably, this effect results from electron motion within their orbital regions rather than promotion to separate excited states, allowing the changes to occur and dissipate nearly as rapidly as the light pulses themselves. However, the optical Kerr effect alone proved insufficient for practical device applications. To amplify the effect, researchers engineered a meta-surface composed of a thin amorphous silicon film with nanoscale pillars smaller than the pump beam’s wavelength. This carefully designed architecture extends light interaction time within the material, strengthening the refractive index change sufficiently to redirect probe beams by angles reaching 13 degrees.
Researchers indicated that current speed limitations stem from the duration of the laser pulses employed to operate the system rather than from fundamental meta-material properties. This assessment suggests potential for further performance improvements, with possible applications extending to emerging photonic concepts including time crystals and synthetic time-varying optical materials. The research team included lead author Claudio Hail, now at UC Berkeley, and Harry Atwater at Caltech, with support from multiple funding agencies.
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