This new method could improve autonomous navigation, material recognition, safety and other applications by collecting more complex thermal data. Researchers have created a new technology using meta-optical devices for thermal imaging. This method provides more detailed information about photographed objects, potentially expanding thermal imaging applications in autonomous navigation, security, thermography, medical imaging, and remote sensing.

“Our method overcomes the challenges of traditional spectral thermal imaging devices, which are often bulky and sensitive due to the use of large filters or interferometers,” said research team leader Zubin Jacob of Purdue University. “We combined meta-optical devices and advanced computational image processing algorithms to create a system that is both compact and robust, and has a wide field of view.”

INSIDE OpticalIn Optica Publishing Group’s high-impact research journal, the authors describe their new spectro-polarimetric decomposition system, which uses an array of rotating metasurfaces to decompose thermal light into its spectral and polarimetric components. This allows the imaging system to capture spectral and polarization details of thermal radiation in addition to the intensity information obtained with conventional thermal imaging.

The researchers showed that the new system can be used with a commercial thermal imaging camera to successfully classify different materials, a task that is often difficult for traditional thermal imaging cameras. The method’s ability to distinguish temperature fluctuations and identify materials based on spectro-polarimetric signatures could help improve safety and efficiency for a variety of applications, including autonomous navigation.

“Traditional autonomous navigation approaches rely heavily on RGB cameras, which have difficulty in harsh environments such as low light or bad weather conditions,” said first author Xuezhi Wang, a postdoctoral researcher at Purdue University. By integrating with thermal detection and ranging technology, our spectropolarimetric thermal camera can provide critical information in these complex scenarios and deliver sharper images than RGB or traditional thermal cameras. “Once we are able to capture real-time video, this technology can significantly improve scene perception and overall safety.”

Do more with a smaller camera

Spectro-polarimetric imaging in long-wave infrared is critical for applications such as night vision, machine vision, gas tracer detection, and thermography. However, modern spectro-polarimetric longwave infrared cameras are bulky and have limited spectral resolution and field of view.

To overcome these limitations, researchers have turned to large-area metasurfaces, which are ultrathin, structured surfaces that can manipulate light in complex ways. After developing rotating dispersive metasurfaces with individual infrared responses, they developed a fabrication process that allowed these metasurfaces to be used to create large-area (2.5 cm diameter) rotating devices suitable for imaging. The resulting spinning stack is less than 10x10x10 cm in size and can be used with a conventional infrared camera.

“The integration of these large-area meta-optical devices with computational imaging algorithms contributed to the efficient reconstruction of the thermal radiation spectrum,” Wang said. said. “This made it possible to create a more compact, reliable and efficient spectropolarimetric thermal imaging system than was previously possible.”

Classification of materials with thermal camera

Purdue researchers used different materials and microstructures, each with unique spectropolarimetric properties, to evaluate their new system. They accurately distinguished different materials and objects using the spectro-polarimetric information obtained with the system. They also demonstrated a threefold increase in material classification accuracy compared to traditional thermal imaging methods, highlighting the efficiency and versatility of the system.

The researchers say the new method could be particularly useful for applications that require detailed thermal imaging. “In security, for example, it could revolutionize airport systems by detecting hidden objects or substances on people,” Wang said. “In addition, its compact and robust design improves its suitability for a variety of environmental conditions, making it particularly useful for applications such as autonomous navigation.”

In addition to working on video capture with the system, researchers are also working to improve the technique’s spectral resolution, transmission efficiency, and image capture and processing speed. They also plan to improve the design of the metasurface to enable more complex manipulation of light for higher spectral resolution. Additionally, since the use of metasurface stacks limits the method to high-temperature objects, they want to extend the method to room-temperature imaging. They plan to do this through techniques such as improved materials, metasurface design, and anti-reflective coatings.