Infrared cameras can capture useful information that the human eye cannot see, such as gases escaping from pipelines, chemicals in the atmosphere, or heat leaking from buildings. However, sophisticated infrared sensing still requires expensive and bulky systems. Researchers at MIT have developed a chip-based optical device that can dynamically control incoming infrared light, acting as a tunable lens to provide additional information for infrared cameras. Each microscopic pixel of the device can control infrared light independently, allowing it to change focus and help cameras detect different signals without moving parts. This system is described in a paper published in Nature Communications.
The researchers built a lab-scale demonstration using mostly conventional manufacturing processes, suggesting it could be implemented at industrial scales. This technology could enable compact, tunable infrared cameras for more dynamic thermal imaging, chemical sensing, pollution monitoring, and even new kinds of optical computing. As first author Cosmin-Constantin Popescu PhD ’25 explains, “This could give us more information as we study space, or help with environmental protections where you want to monitor for specific compounds in the atmosphere.”
Recently, researchers have developed ways to dynamically control light by etching tiny, precise patterns on transparent materials known as “metasurfaces.” Hu’s research group at MIT has experimented with metasurfaces that shift from solid to liquid upon heating, which can be harnessed to control how materials interact with light.
For their new study, the researchers aimed to control light independently at each microscopic pixel. “Most active metasurfaces trying to do single-pixel tuning need wires going to every pixel, and how you route the wires becomes a big issue,” Hu explains. The researchers also wanted to work with mid-infrared wavelengths, which are useful for detecting heat signatures and molecules like methane and propane.
To build their system, the researchers adapted a common display approach where two layers of copper wires are placed perpendicularly to each other. Below the wires is a layer of doped silicon that generates heat at the cross points. This heat is used to switch each pixel between crystalline and amorphous structures, changing how the material interacts with incoming infrared light. The silicon also includes a diode selector to prevent unintended currents from leaking through neighboring pixels.
“Calculations show this architecture allows us to scale to potentially millions of pixels without issues with unintended currents,” Hu says. The key innovation is this crossbar architecture, which creates a scalable way to increase pixel-level switching of metasurfaces. This is the first time this architecture has been used for active phase-change metasurfaces.
The researchers created a 6-by-6 metasurface pixel array and tested their system, finding it could reliably switch on and off. They believe integrating part of their design into existing semiconductor manufacturing will help it move beyond a research prototype. “As you want to scale up, you need something that’s part of a consistent process,” Hu notes.
The team is working to add more pixels to their array and develop more robust versions so they can capture more infrared information. “In many cases when taking images, you have prior knowledge of what you’re looking for,” Hu says. “This could enable more effective optical computing, where metasurfaces are used to encode network weights in neural networks.”
Blogger's Review: This technological breakthrough enhances the flexibility and precision of infrared imaging, significantly improving gas and heat detection capabilities. It holds promise for vital applications in environmental monitoring and military contexts, and we look forward to its acceleration towards industrial implementation.