A tiny metasurface chip can turn invisible infrared light into steerable visible beams, opening the door to powerful new optical technologies.

Developing extremely small devices that can precisely guide and manipulate light is critical for many emerging technologies. Scientists at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) have now demonstrated an important advance by creating a metasurface that can transform invisible infrared light into visible light and send it in different directions—without any moving parts. Their results are described in a study published in the journal eLight.

How the Ultra-Thin Metasurface Chip Works

The new metasurface is built as an ultra-thin chip covered with tiny patterned structures that are smaller than the wavelength of light itself. When the surface is illuminated by an infrared laser, the chip converts the incoming light into a higher color (or frequency). The newly generated light leaves the chip as a narrow beam whose direction can be adjusted simply by changing the polarization of the incoming light.

During testing, the researchers converted infrared light with a wavelength of about 1530 nanometers into visible green light around 510 nanometers. The infrared wavelength used in the experiments is similar to light commonly used in fiber optic communication systems. The team was also able to direct the green light beam toward specific angles.

“Think of it as a flat, microscopic spotlight that not only changes the color of light but also points the beam wherever you want, all on a single chip,” said Andrea Alù, founding director of the CUNY ASRC Photonics Initiative and Distinguished Professor at the CUNY Graduate Center. “By making different parts of the surface work together, we get both very efficient conversion of light and precise control over where that light goes.”

Overcoming a Longstanding Metasurface Tradeoff

Engineers have used metasurfaces for years to bend, focus, and reshape light using flat materials engineered at the nanoscale. These devices, however, usually face a tradeoff:

• Structures that control light at each pixel of the surface are flexible but not very efficient at boosting light.
• Structures that allow light waves to spread and interact across the whole surface can be very efficient, but they lose fine control over the beam shape.

The device created at CUNY is the first to combine both advantages for nonlinear light generation, a process in which one color of light is converted into another. It relies on a special collective resonance—called a quasi–bound state in the continuum—that traps and strengthens the incoming infrared light across the entire surface. At the same time, each tiny element on the metasurface is rotated according to a carefully designed pattern, giving the outgoing light a position-dependent phase similar to the effect of a built-in lens or prism.

Generating and Steering Third Harmonic Light

Because of this structure, the chip produces third-harmonic light—light whose frequency is three times that of the incoming beam—while also steering the resulting beam into chosen directions. When the polarization of the incoming light is reversed, the direction of the outgoing beam also reverses. This provides a simple control mechanism for beam steering.

The system produces a third harmonic signal that is about 100 times more efficient than similar devices capable of shaping beams but lacking these collective resonances.

Toward Compact Light Sources and On-Chip Photonics

The ability to efficiently create and guide new colors of light using a flat chip could enable a wide range of future technologies.

“This platform opens a path to ultra-compact light sources and beam-steering elements for technologies like LiDAR, quantum light generation, and optical signal processing, all integrated directly on a chip,” said lead author Michele Cotrufo, a former postdoctoral fellow at CUNY and now an assistant professor at the University of Rochester. “Because the concept is driven by geometry, not by one specific material, it can be applied to many other nonlinear materials and across different colors of light, including the ultraviolet.”

According to the researchers, future versions of the technology could stack or combine several metasurfaces that are each tuned slightly differently. This approach could allow the system to operate efficiently across a broader range of wavelengths.

Reference: “Nonlinear nonlocal metasurfaces” by Michele Cotrufo, Luca Carletti, Adam Overvig and Andrea Alù, 2 February 2026, eLight.
DOI: 10.1186/s43593-025-00116-7

The work received support from the U.S. Department of Defense, the Simons Foundation, and the European Research Council.

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