EPFL Scientists Unveil Chiral Metasurfaces for Secure Light Control

In a groundbreaking study published in *Nature Communications* on July 16, 2025, researchers from the École Polytechnique Fédérale de Lausanne (EPFL) have unveiled a novel optical metasurface designed to control light through the principles of chirality. This technology holds significant potential for applications in secure data encryption, biosensing, and quantum computing.

Chirality, a fundamental property of molecular structures, refers to the distinction between left-handed and right-handed forms of a shape. This concept is crucial in various fields, including biology and materials science, where the handedness of molecules can drastically affect their function. For instance, while most amino acids are left-handed, sugars are predominantly right-handed, and the reversal of a molecule's chirality can lead to harmful effects, such as rendering a drug ineffective.

The researchers at EPFL's Bionanophotonic Systems Laboratory, led by Professor Hatice Altug, developed a 'chiral design toolkit' that enables precise control over the chirality of artificial optical structures known as metasurfaces. These metasurfaces are composed of a two-dimensional lattice of tiny elements called meta-atoms, which can be oriented in various ways to manipulate the interaction with polarized light. According to Altug, "Our approach is elegantly simple yet more powerful than previous methods, which relied on complex geometries to control light. We utilize the interplay between the meta-atom's shape and the symmetry of the metasurface lattice."

In a proof-of-concept experiment, the team encoded two distinct images onto a metasurface optimized for the mid-infrared range of the electromagnetic spectrum. One image, representing an Australian cockatoo, was encoded through the size of the meta-atoms, while the second, revealing the Matterhorn, was based on the orientation of the meta-atoms when illuminated by circularly polarized light. This innovative method resulted in a dual-layer watermark that is invisible to the naked eye, paving the way for enhanced security applications, including anti-counterfeiting and camouflage technologies.

The potential implications of this research extend beyond encryption. The ability to map chiral responses across extensive surfaces could significantly enhance biosensing capabilities, allowing for the detection of drug compositions or purity levels from minuscule samples. As researcher Felix Richter noted, "Chirality is inherent in nature, and distinguishing between left- and right-handed molecules is essential, particularly in the pharmaceutical industry, where it can mean the difference between a medicine and a toxin."

The findings from this study represent a significant step forward in the field of optical engineering. The EPFL team continues to explore the broader applications of chiral metasurfaces in various high-tech industries, emphasizing the importance of this research in advancing secure communication technologies and improving drug safety. As the field evolves, the collaboration between EPFL and Australian scientists highlights an international commitment to leveraging advanced materials science for practical, real-world applications.

This research not only showcases the innovative capabilities of current optical technologies but also serves as a reminder of the intricate relationship between physics and chemistry in the development of new scientific solutions.