Researchers from TMOS, the ARC Centre of Excellence for Trans­formative Meta-Optical Systems, have made signi­ficant progress in their journey to deliver a new approach to night vision technology, creating an infrared filter that is thinner than a piece of cling wrap, and that could one day be placed on everyday eyewear, allowing the user to view the infrared and visible light spectrum at the same time. Night vision devices have primarily been used by the military, hunting enthu­siasts willing to lug around multi­­purpose binoculars, or photo­­graphers happy to carry around heavy lenses. This is due to the weight and bulk of the techno­logy. The average person is not going for a night-time run with an additional kilo strapped to their forehead.

Miniaturizing night vision could lead to widespread adoption. Creating night vision filters that weigh less than a gram and can sit as a film across a pair of tradi­tional spectacles opens up new, everyday appli­cations. Consumer night vision glasses that allow the user to see the visible and infrared spectrum at the same time could result in safer driving in the dark, safer night time walks, and less hassle working in low-light conditions that currently require bulky and often uncomfortable headlamps. Now, TMOS researchers from the Australian National University demonstrate enhanced infrared vision non-linear upcon­version technology using a non-local lithium niobate metasurface.

Traditional night vision technology requires infrared photons to pass through a lens, then encounter a photo­cathode that transforms these photons into electrons, which then go through a micro­channel plate to increase the number of electrons generated. These electrons which travel through a phosphor screen to be reconverted back to photons, producing an inten­sified visible image that can be seen by eye. These elements require cryogenic cooling to prevent thermal noise from also being intensified. A high-quality night vision system, like the one described above, is heavy and bulky. In addition, these systems often block the visible light.

The metasurface-based upconversion techno­logy requires fewer elements, drastically reducing its footprint. Photons pass through a single resonant meta­surface where they are mixed with a pump beam. The resonant metasurface enhances the energy of the photons, drawing them into the visible light spectrum – no conversion of electrons needed. It also works at room temperature, elimi­nating the need for bulky and heavy cooling systems. In addition, traditional infrared and visible imaging systems cannot produce identical images, as they capture images from each spectrum side-by-side. By using up-conversion techno­logy, imaging systems can capture both the visible and non-visible in one image.

The work is an improvement on the researchers’ original technology, which featured a gallium arsenide metasurface. Their new metasurface is made from lithium niobate, which is fully transparent in the visible range, making it far more effi­cient. In addition, the photon beam is spread over a wider surface area, limiting angular loss of data. Laura Valencia Molina says, “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.”

Rocio Camacho Morales says, “This is the first demonstration of high resolution up-conversion imaging from 1550 nanometers infrared to visible 550 nanometers light in a non-local metasurface. We choose these wavelengths because 1550 nanometer light is commonly used for telecommuni­cations, and 550 nanometer 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 says, “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.” (Source: TMOS / ARC)

Reference: L. V. Molina et al.: Enhanced Infrared Vision by Nonlinear Up-Conversion in Nonlocal Metasurfaces, Adv. Mat., online 23 May 2024; DOI: 10.1002/adma.202402777

Link: ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Dept. of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, Australia