Scientists from Linköping University in Sweden have announced an optical breakthrough in tunable polymer (plastic) metalenses that control light like traditional glass lenses with enough precision to create realistic holograms, and invisibility materials.
A better understanding of the unique properties of controllable flat optics like metalenses, including their strength, scalability, and tunability, could lead to several other advanced optical applications, including biomedical imaging and quantum sensing.
Tunable Metalenses and Realistic Holograms
When engineers want to control the behavior of light, most employ traditional glass lenses. While these lenses are well-suited for most applications, such as telescopes, microscopes, cameras, eyeglasses, and contacts, they have inherent limitations. For example, lenses become increasingly less effective when they are scaled down to create holographic displays.
One potential alternative to lenses is flat optics. According to Magnus Jonsson, a professor of applied physics at Linköping University, flat optics employ cutting-edge metasurfaces to produce “lenses” capable of controlling light at much smaller scales.
“Metasurfaces work in a way that nanostructures are placed in patterns on a flat surface and become receivers for light,” Jonsson explained. “Each receiver, or antenna, captures the light in a certain way, and together these nanostructures can allow the light to be controlled as you desire.”
Still, metasurfaces also have limitations that make replacing traditional lenses impractical. Now, Jonsson and colleagues believe they may have finally found a solution.
One Word: Plastics!
Jonsson and Dongqing Lin, a postdoc student and principal author of the paper detailing the team’s research, listened to feedback from people in research and industry to learn the primary shortcomings of flat surface optics like metalenses. The most common requests were the ability to turn the surface on and off dynamically and to change the focal point of the light.
Researchers Dongqing Lin and Magnus Jonsson examine a sample by the scanning electron microscope at Linköping University. Credit: Thor Balkhed.
A direct examination of the most commonly available optical metasurfaces found that the primary materials used in their manufacture, such as gold and titanium dioxide, made ‘tuning’ the light’s focal point after their manufacture impossible. The materials used in traditional optical metasurfaces also limit the ability to turn them on and off.
The situation changed in 2019 when Professor Johnson’s team showed that conductive plastics could be the ultimate answer. Unlike metals, the material was physically alterable after manufacture, allowing for the changing of the light’s focal point. The team also showed the ability to turn the polymer metalenses on and off. Nonetheless, the team says that the performance of plastic-based lenses was “not comparable to metasurfaces made from traditional materials.”
In their latest study, the tea claims an increase in performance “up to tenfold.” This increase is mostly credited to relocating the antennas to produce “collective lattice resonance,” which amplifies the light interaction between antennas.
Visible Light and Potential Applications
In the study’s conclusion, Jonsson and colleagues note that their experiments confirmed the ability to control light in the infrared spectrum. They hope to explore controlling light in the visible spectrum in upcoming experiments.
Ultimately, the team believes the ability to scale optical metasurfaces could offer the precision control of light needed to produce realistic holograms and invisibility materials. Whatever the applications, they feel their plastic metalenses show that these materials are ready for commercial and industrial use.
“We show that metasurfaces made of conducting polymers seem to be able to provide sufficiently high performance to be relevant for practical applications,” Lin said.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.