Harnessing the Power of Twisted Light

Did you know that light can twist? Scientists have uncovered that light beams can be circularly polarized, spiraling either left or right. This fascinating property allows researchers to uncover hidden details about materials based on how they interact with twisted light. However, the challenge has been that the effects of chirality—how substances respond to these twisted waves—is often minimal, making precise control a daunting task.

Innovative Technology at EPFL and Beyond

Now, a groundbreaking collaboration between the Bionanophotonic Systems Laboratory at EPFL and scientists from Australia has led to the creation of artificial optical structures known as metasurfaces. These 2D lattices are constructed from tiny elements, dubbed meta-atoms, that can be manipulated to exhibit chiral properties. By simply adjusting the orientation of these meta-atoms, the team can control how the metasurfaces interact with polarized light.

Hatice Altug, head of the Bionanophotonics Lab, describes their 'chiral design toolkit' as both elegant and powerful, simplifying the complex tasks of controlling light by utilizing the relationship between the shapes of meta-atoms and the lattice's symmetry.

Invisible Images: A Major Breakthrough

Their innovative metasurface, composed of germanium and calcium difluoride, features a continuous gradient of meta-atom orientations across its surface. This configuration allows the chip to react uniquely to polarized light.

In an exciting proof-of-concept experiment, the researchers successfully encoded two distinct images on the metasurface, visible only under specific light conditions. The first, an image of an Australian cockatoo, was cleverly encoded in the size of the meta-atoms, while the second, a stunning depiction of the Swiss Matterhorn, emerged when illuminated with circularly polarized light.

This dual-layer watermarking technique—fully invisible to the naked eye—opens doors to advanced applications in anti-counterfeiting, security, and even camouflage, as highlighted by lab researcher Ivan Sinev.

Endless Possibilities for the Future

But the implications don’t stop there. The researchers believe this innovative approach could revolutionize quantum technologies, where polarized light often plays a crucial role in computations.

Additionally, these chiral metastructures could greatly enhance biosensing capabilities, enabling the detection of drug composition and purity from tiny samples. "In nature, chirality is key— distinguishing between left and right-handed molecules could mean the difference between a life-saving drug and a harmful toxin," adds researcher Felix Richter.

With such promising potential, this technology could soon change how we think about light, security, and health.