Chinese researchers have developed an infrared contact lens that makes night vision possible. Nanoparticles make the previously invisible light range visible to the human eye.
Light consists of individual particles that propagate in waves. The wavelength determines the color and energy of the light.
The human eye can only perceive a small section of this spectrum, approximately the range between 400 and 700 nanometers.
Because of that, we humans are unable to see the infrared range, with its longer wavelengths of 750 nanometers to one millimeter.
So in order to see infrared light, we have needed comparatively bulky night-vision goggles or night-vision devices with their own energy source — until now.
Infrared contact lenses from China
Researchers at the University of Science and Technology in Hefei, eastern China, have now developed a contact lens that converts infrared light into visible light, enabling humans to see in the dark.
Yuqian Ma and his team have combined conventional soft contact lenses with 45 nanometer particles consisting of gold, sodium gadolinium fluoride, ytterbium and erbium ions.
The upconversion contact lenses (UCLs) convert infrared light with wavelengths between 800 and 1,600 nanometers into visible light, the team wrote in the scientific journal Cell.
The nanoparticles enrich the long infrared light waves with energy. In doing so, they convert infrared light into three primary colors, making them visible to the human eye.
One drawback is that the resulting images are very blurred because the nanoparticles in the lenses scatter the light, which the team was able to partially compensate for by adding additional lenses.
However, the infrared contact lenses are still nowhere near as powerful as night vision goggles, which amplify weak infrared signals, making them visible.
Even better vision with eyes closed
The team first injected nanoparticles into the retinas of mice and their behavior showed that they could see in the dark.
The newly developed contact lenses are much more practical because they are non-invasive — meaning no injections into our retinas.
In tests, humans were able to recognize patterns, letters and flashing infrared signals in the dark. And the infrared lenses work even better with closed eyes, because the infrared light can easily penetrate the eyelids and image generation is not disturbed by normal visible light.
Animal infrared capabilities
Several animal species are able to perceive infrared light, which is extremely helpful when hunting in the dark. They do not see infrared light as "light" in the sense of human vision. Instead they perceive the heat radiation emitted by objects.
Warm-blooded animals — such as humans, other mammals and birds — cannot see infrared light because their eyes do not have the appropriate receptors and their body's own heat radiation would also interfere with the perception of infrared light.
Big question about the benefits
As fascinating as the Chinese innovation is, it remains to be seen how it could be used in everyday life.
According to the developers, the lenses could be used in surgical procedures, in the field of encryption or cryptography, or for counterfeit protection.
This is because infrared light is what makes invisible features or inks visible on documents, for example.
The lenses could also be used to rescue people in poor visibility conditions because they make heat-emitting objects visible. However, many critics doubt this, as night vision devices are much easier to use, and are also significantly more powerful.
This article was originally written in German.
Source:
Near-infrared spatiotemporal color vision in humans enabled by upconversion contact lenses
https://www.cell.com/cell/fulltext/S0092-8674(25)00454-4
Alexander Freund Science editor with a focus on archaeology, history and health
Ultra-thin lenses that make infrared light visible
ETH Zurich
image:
Infrared light passes through the metal lens and is converted into violet light and focussed in a focal point due to the material and the special surface structures – enlarged in the magnifying glass.
view moreCredit: Ülle-Linda Talts, ETH Zurich
Lenses are the most widely used optical devices. Camera lens or objectives, for example, produce a sharp photo or video by directing light at a focal point. The speed of evolution made in the field of optics in recent decades is exemplified by the transformation of conventional bulky cameras into today’s compact smartphone cameras.
Even high-performance smartphone cameras still require a stack of lenses that often account for the thickest part of the phone. This size constraint is an inherent feature of classic lens design – a thick lens is crucial for bending light to capture a sharp image on the camera sensor.
Major strides in the field of optics over the past ten years have sought to overcome this limitation and have come up with a solution in the form of metalenses. They are flat, perform in the same way as normal lenses and are not only 40 times thinner than an average human hair but also lightweight as they do not need to be made of glass.
A special metasurface composed of structures a mere hundred nanometres in width and height (one nanometre is one billionth of a metre) modifies the direction of light. Using such nanostructures researchers can radically reduce the size of a lens and make it more compact.
When combined with special materials, these nanostructures can be used to explore other unusual properties of light. One example is nonlinear optics, where light is converted from one colour into another. A green laser pen works according to this principle: infrared light goes through a high-quality crystalline material and generates light of half the wavelength – in this case green light. One well-known material that produces such effects is lithium niobate. This is used in the telecommunications industry to create components that interface electronics with optical fibres.
Rachel Grange, a professor at the Institute for Quantum Electronics at ETH Zurich, conducts research into the fabrication of nanostructures with such materials. She and her team have developed a new process that allows lithium niobate to be used to create metalenses. The study has recently been published in the journal Advanced Materials.
For her new method, the physicist combines chemical synthesis with precision nanoengineering. “The solution containing the precursors for lithium niobate crystals can be stamped while still in a liquid state. It works in a similar way to Gutenberg’s printing press,” co-first author Ülle-Linda Talts, a doctoral student working with Rachel Grange, explains. Once the material is heated to 600°C, it takes on crystalline properties that enable the conversion of light as in the case of the green laser pen.
The process has several advantages. Producing lithium niobate nanostructures is difficult using conventional methods as it is exceptionally stable and hard. According to the researchers, this technique is suitable for mass production as an inverse mould can be used multiple times, allowing the printing of as many metalenses as needed. It is also much more cost-effective and faster to fabricate than other lithium niobate miniaturised optical devices.
Ultra-thin lenses that generate new light
Using this technique, the ETH researchers in Grange’s group succeeded in creating the first lithium niobate metalenses with precisely engineered nanostructures. While functioning as normal light focusing lenses, these devices can simultaneously change the wavelength of laser light. When infrared light with a wavelength of 800 nanometres is sent through the metalens, visible radiation with a wavelength of 400 nanometres emerges on the other side and is directed at a designated point.
This magic of light conversion, as Rachel Grange calls it, is only made possible by the special structure of the ultra-thin metalens and its composition of a material that allows the occurrence of what is known as the nonlinear optical effect. This effect is not limited to a defined laser wavelength, making the process highly versatile in a broad range of applications.
From counterfeit-proof banknotes to next-generation microscopy tools
Metalenses and similar hologram-generating nanostructures could be used as security features to render banknotes and securities counterfeit-proof and to guarantee the authenticity of artworks. Their exact structures are too small to be seen using visible light, while their nonlinear material properties allow highly reliable authentication.
Researchers can also use simple camera detectors to convert and steer the emission of laser light to make infrared light – in sensors, for example – visible. Or for reducing the equipment needed for deep-UV light patterning in state-of-the-art electronics fabrication.
The field of such ultra-thin optical elements – known as metasurfaces – is a relatively young branch of research at the interface between physics, materials science and chemistry. “We have only scratched the surface so far and are very excited to see how much of an impact this type of new cost-effective technology will have in the future,” emphasises Grange.
Journal
Advanced Materials
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Scalable Lithium Niobate Nanoimprinting for Nonlinear Metalenses
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