In a lab in Zurich, scientists have built something that, at first glance, shouldn’t be possible.
When a beam of infrared light strikes their ultra-thin lens—barely thicker than a red blood cell—it emerges on the other side transformed. The lens shrinks the wavelength in half, shifting invisible infrared into visible violet, and focuses it into a sharp point.
This extraordinary feat, recently published in Advanced Materials, may sound like science fiction. But it’s rooted in a new way of shaping and building lenses from tiny, tooth-like structures carved into a special crystal using a technique borrowed from the printing press.
The result is a new kind of lens that can make the invisible world visible—and it might change how we make everything from smartphone cameras to anti-counterfeit banknotes.
A Flat Lens with Superpowers
For centuries, lenses have looked virtually the same: curved hunks of glass that bend light toward a focal point.
The ETH team, led by Rachel Grange, a professor at the Institute for Quantum Electronics at ETH Zurich, and doctoral student Ülle-Linda Talts, took a different route. Instead, they designed a flat metamaterial (a man-made material designed to have properties not found in nature) whose surface is patterned with nanostructures. These are called metalenses—wafer-thin sheets that manipulate light with sub-wavelength precision.
In this case, they went a step further. The researchers didn’t just bend light; they changed its color by harnessing a property called “second-harmonic generation.” That’s when two photons of a lower-energy light merge into one of higher energy—like taking two long, red threads and twisting them into a short, bright violet one.
To do this, the lens’ materials had to be something special.
Enter Lithium Niobate
The hero material in this story is lithium niobate—a workhorse in optical telecommunications with the ability to manipulate light through nonlinear effects. But until now, fabricating it into precise, nanoscale shapes has been notoriously difficult.
That’s because lithium niobate is chemically and physically stubborn. So, instead of chiseling it, the team developed a new recipe—a printable version of lithium niobate using a sol-gel solution. In its liquid form, the material can be molded into nanostructures using soft nanoimprint lithography, a method akin to stamping text onto paper. Once shaped and baked at 600°C, it crystallizes into the same kind of nonlinear optical material found in telecom-grade devices.
“The solution containing the precursors for lithium niobate crystals can be stamped while still in a liquid state,” Talts said. “It works in a similar way to Gutenberg’s printing press.”
A Focal Point of Light, and Possibility
The result is a metalens less than a micron thick that focuses incoming infrared light and simultaneously turns it into visible violet. When the team tested it with a near-infrared laser at 800 nanometers, the output was a tight focal point at 400 nanometers—a direct conversion visible to the naked eye.
The performance was remarkable: The lens increased the intensity of the output light by more than 30 times at the focal point. And it did this across a broad range of wavelengths, from the near-infrared to the near-ultraviolet, without relying on fragile resonance effects.
What makes this especially striking is that it works using polycrystalline lithium niobate—composed of many tiny, randomly oriented domains. Each nanostructure, or “meta-atom,” acts like a miniature antenna, collectively steering and converting the light through a process based on the geometry of its layout.
Possible Applications
For now, this might seem like an achievement confined to physics labs. But the implications are vast.
In the world of security, such metalenses could be embedded into documents or currency. Their structure is invisible under normal light but could produce unmistakable optical signatures when illuminated with a laser. It could provide a powerful anti-counterfeiting tool.
In imaging and sensing, these devices could allow tiny cameras to detect infrared light—a crucial ability for night vision, autonomous vehicles, and medical diagnostics—without bulky optics or complex devices.
In semiconductor manufacturing, they might reduce the cost and challenges of deep ultraviolet lithography, the process that etches the patterns of modern microchips.
And in fundamental science, the platform opens doors for advanced quantum optics, including generating entangled photons through a process called spontaneous parametric down-conversion, which is useful in quantum communication and computation.
Despite the breakthrough, this is still a young technology. The resolution of the new lens is already impressive, but there’s room for improvement. Future designs could incorporate advanced resonances or fine-tuned nanostructure geometries to boost efficiency even further.
The team is also exploring how to make the nanocrystals larger and reduce porosity, which would enhance their nonlinear performance. “We have only scratched the surface so far,” Grange said.
Still, the study marks a milestone in optics—a proof that flat, printable lenses can transform light. As our devices grow smaller and smarter, the light that powers them must also bend to new rules. With a lens thinner than a human hair, ETH physicists have shown that even light can be reshaped from the ground up.
