Until now, satellites and space payloads have required new optical filters and sensors to be designed whenever their missions changed. A future is now on the horizon in which a single ultra-compact optical chip can perform a variety of roles—including those of a thermal imaging sensor, spectrometer, and infrared camera—using electrical signals alone.
KAIST (President Choongsik Bae) announced on 14th of July that a research team led by Professor Hyun Jung Kim from the Department of Aerospace Engineering, in collaboration with a research team led by Professor Juejun Hu at the Massachusetts Institute of Technology (MIT), has demonstrated the first transmissive mid-infrared amplitude-only spatial light modulator based on a scalable two-dimensional, electrically addressable metasurface architecture.
The key achievement of this research is that a single optical chip can perform a variety of sensor functions using electrical signals alone. Previously, new optical filters and sensors had to be fabricated for each new mission. In the future, the technology is expected to enable the realization of "software-defined sensors," whose functions can be changed without replacing the hardware.
The device developed by the research team is a transmissive mid-infrared spatial light modulator, or SLM, based on a metasurface. A metasurface is an ultrathin optical structure that uses microscopic patterns much smaller than the width of a human hair to freely control the intensity, direction, and wavelength of light.
A spatial light modulator controls the spatial distribution of light on a pixel-by-pixel basis. In the present device, each pixel switches the intensity of transmitted mid-infrared light between two programmed states. The research team succeeded, for the first time in the world, in electrically and independently controlling each individual pixel.
Conventional spatial light modulators face significant limitations in the mid-infrared. Liquid-crystal-based devices suffer from material absorption and relatively slow response, while digital micromirror devices operate in reflection. Transmissive mid-infrared SLMs have therefore remained largely unexplored. This has limited their application to satellite sensors, ultra-compact spectrometers—which analyze light according to wavelength—and adaptive optical systems, which automatically adjust their optical performance in response to changes in the surrounding environment.
To address these limitations, the researchers used GSST—Ge₂Sb₂Se₄Te, or germanium-antimony-selenium-tellurium—an optical phase-change material (PCM) whose light transmittance changes when it receives an electrical signal.
Once GSST receives an electrical signal, it retains its state and continues to maintain the same optical performance even after the power is turned off. This nonvolatile characteristic eliminates the need for a continuous power supply, making the material suitable for satellites and space payloads, where the available electrical power is limited.
As the number of pixels on an optical chip increases, electrical current can flow into pixels other than the selected pixel, causing unintended pixels to operate as well. This is known as the "sneak-path" problem.
The research team solved this problem by integrating a silicon PIN diode into each pixel. A PIN diode is a semiconductor device that allows electrical current to flow only to the intended pixel. This enabled the researchers to accurately select and control only the desired pixels.
Using this approach, the team independently controlled all the pixels in a 6 × 6 pixel array and successfully produced desired optical patterns. The device also maintained stable performance after more than 16,700 switching cycles, demonstrating approximately 13 times greater endurance than previous technology.
The device was fabricated using silicon photonics, a technology that produces optical devices through standard semiconductor manufacturing processes. This makes it relatively easy to scale the technology to larger optical chips containing hundreds, thousands, or even more pixels.
The current device controls only the amount of transmitted light. In the future, however, more sophisticated metasurface designs are expected to enable the technology to develop into "universal reconfigurable optics," capable of freely controlling the direction and polarization of light as well.
The greatest significance of this research is that it presents a new concept in which "optics, too, can be changed like software." In other words, the study provides a foundation for programmable optical hardware that could support different sensing functions through reconfiguration rather than hardware replacement.
In the future, this is expected to usher in an era of software-defined sensors, in which a single optical chip can perform different functions depending on the situation, serving as a thermal imaging sensor, spectrometer, infrared camera, or optical communication device.
Once commercialized, the technology is expected to make it possible to implement a wide range of optical systems on a single platform. Potential applications include satellites and space payloads, launch-vehicle health diagnostics, thermal monitoring of space stations, measurement of in-space manufacturing processes, infrared imaging, and optical communications.
This research is an achievement that further advances MIT–NASA collaborative research initiated in 2018, when Professor Hyun Jung Kim was working as a researcher at the National Aeronautics and Space Administration (NASA), and subsequently continued at KAIST.
Building on this foundation, KAIST's STAR Lab and Professor Juejun Hu's research team at MIT are currently conducting joint research on active meta-optics, silicon photonics, and space sensor systems, with the goal of applying the technology in actual space environments.
The two teams have established a full-cycle international collaborative research framework encompassing material development, chip design and fabrication, sensor-system integration, space-environment verification, and future flight demonstrations.
Professor Kim's research team is now developing the technology into an operational space sensor. Under the Ministry of Science and ICT's Young Researcher Program, the team is developing an ultra-precise system for measuring the surface temperature of launch vehicles.
The research is also being expanded through the "Space Services and Manufacturing Research Center" under the Innovation Research Center Program. The team is conducting research to develop the technology into a common optical platform that can be used for space-station thermal monitoring, anomaly diagnosis, measurement of in-space manufacturing processes, and optical communications.
"This research is not simply about creating one more new optical device," said Professor Kim. "It presents the foundation for an era of software-defined sensors, in which a single optical chip performs a variety of functions depending on the mission."
"By combining MIT's nanophotonics technology—which uses nanostructures to control light—with KAIST's space sensor technology, we plan to develop this technology into an actual space system," she added.
The research was published online in the international journal Nature Communications on July 7.
Paper title: "Two-Dimensional Pixel-Level Addressable Mid-Infrared Metasurface Spatial Light Modulator"
DOI: 10.1038/s41467-026-75346-5
This work was funded by the Air Force SBIR Program under contract FA2394-23-C-5076, the National Science Foundation under awards 2329088 and 2132929, and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-00515651 and RS-2025-02213804).
