Scientists at EPFL in Switzerland, together with colleagues in Australia, have come up with a new way to control chirality in light using specially designed surfaces called metasurfaces. Chirality, or “handedness,” is the idea that some things are mirror images but cannot be perfectly overlapped, like left and right hands. In biology, this matters a lot: DNA and sugars are right-handed, while amino acids are left-handed. Switching the handedness of a molecule can make a nutrient useless or even turn a drug harmful. Light itself can also be left- or right-handed when it is circularly polarized, meaning its electric field twists through space in a spiral.
The problem is that materials usually interact only very weakly with this twisted light, so controlling chirality has been difficult. The EPFL team tackled this by building metasurfaces, which are flat lattices made of tiny building blocks called meta-atoms. By changing the orientation of these meta-atoms and arranging them in different lattice patterns, the researchers could tune how the surface responds to polarized light. Their method works across all five possible planar Bravais symmetries, making it a universal design strategy.
The metasurface they built used germanium and calcium difluoride and contained a gradient of meta-atoms whose orientations varied smoothly across the chip. This setup allowed them to produce predictable chiral responses that could be adjusted by simple changes in parameters. In one experiment, they encoded two images at once in the mid-infrared range. A picture of an Australian cockatoo was encoded in the size of the meta-atoms and could be seen with unpolarized light. A second image of the Swiss Matterhorn was encoded in the orientation of the meta-atoms and only appeared when circularly polarized light was used. This showed that the metasurface could encode information in both transmission and circular dichroism at the same time.
This dual encoding acts like a hidden watermark, which could be useful for anticounterfeiting, camouflage, and secure data storage like optical encryption. But the applications go further. Chiral metasurfaces can help control structured light for biosensing, photochemistry, holography, and quantum photonics. For example, quantum technologies often rely on polarized light to perform calculations, and biosensing depends on being able to tell left- and right-handed molecules apart. The ability to map chiral responses across large surfaces could make it easier to test drug composition or purity from very small samples.
The researchers describe their approach as a “chiral design toolkit” that is simpler than earlier methods, which relied on complex meta-atom shapes. Instead, they focus on the balance between meta-atom geometry and lattice symmetry. This gives scientists a flexible way to design chiral metastructures on demand, opening up new possibilities in life sciences, quantum optics, and advanced optical technologies.
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