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New Infrared Filter Promises Safer Night Activities

In a recent study published in the journal Advanced Materials, researchers from the TMOS, the ARC Centre of Excellence for Transformative Meta-Optical Systems, have developed an infrared filter that is thinner than a piece of cling wrap and that, in the future, may be worn on regular eyeglasses to enable simultaneous viewing of the visible and infrared light spectrum.

New Infrared Filter Promises Safer Night Activities

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Night vision devices tend to be used by the military, hunting enthusiasts willing to carry multipurpose binoculars, or photographers happy to carry heavy lenses. This is due to the technology's weight and bulk. The average person is not going for a night-time run with an additional kilo strapped to their forehead.

Therefore, miniaturizing night vision technology could help expand its adoption. Developing night vision filters that are less than a gram in weight and can sit as a film across a pair of traditional spectacles opens up new, everyday applications. 

Consumer night vision glasses that enable the wearer to see the visible and infrared spectrum simultaneously could result in safer driving in the dark, safer nighttime strolls, and easier working conditions for those who have to work in low light.

Conventional night vision technology requires infrared photons to pass through a lens and then meet a photocathode that changes these photons into electrons. These electrons then go through a microchannel plate to increase the number of electrons generated. These electrons travel through a phosphor screen to be converted back to photons, producing an intensified visible image that can be seen by the eye.

This requires cryogenic cooling to prevent thermal noise from intensifying. A high-quality night vision system, like the one described above, is bulky and heavy. Additionally, these systems often block visible light.

In contrast, the team's new technology has a drastically reduced footprint as fewer elements are needed. Photons pass through a single resonant metasurface, where they are mixed with a pump beam. The resonant metasurface increased the energy of the photons, bringing them into the visible light spectrum—no conversion of electrons is needed. This method also works at room temperature, removing the cumbersome need for cooling systems.

In addition, traditional infrared and visible imaging systems struggle when it comes to producing identical images, as they capture images from each spectrum side-by-side. Using up-conversion technology, imaging systems can now capture both the visible and non-visible in one image.

This work improves on the team’s original technology, which was designed using a gallium arsenide metasurface. Their new metasurface is made from lithium niobate, which is fully transparent in the visible range, making it much more efficient. Additionally, the photon beam is spread over a wider surface area, limiting the angular loss of data.

People have said that high efficiency up-conversion of infrared to visible is impossible because of the amount of information not collected due to the angular loss that is inherent in non-local metasurfaces. We overcome these limitations and experimentally demonstrate high efficiency image up-conversion.

Laura Valencia Molina, Study Lead Author, Australian National University

Rocio Camacho Morales added, “This is the first demonstration of high resolution up-conversion imaging from 1550 nm infrared to visible 550 nm light in a non-local metasurface. We choose these wavelengths because 1550 nm, an infrared light, is commonly used for telecommunications, and 550 nm is visible light to which human eyes are highly sensitive. Future research will include expanding the range of wavelengths the device is sensitive to, aiming to obtain broadband IR imaging, as well as exploring image processing, including edge detection.”

Chief Investigator Dragomir Neshev stated, “These results promise significant opportunities for the surveillance, autonomous navigation, and biological imaging industries, amongst others. Decreasing the size weight and power requirements of night vision technology is an example of how meta-optics, and the work TMOS is doing, is crucial to Industry 4.0 and the future extreme miniaturization of technology.”

Journal Reference:

‌Molina, L. V., (2024) Enhanced Infrared Vision by Nonlinear Up‐Conversion in Nonlocal Metasurfaces. Advanced Materials. doi:10.1002/adma.202402777

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