Light in the mid-infrared (mid-IR) portion of the electromagnetic spectrum plays a key role in modern sensing. Because molecules interact with this kind of light in specific ways, researchers use technologies like mid-IR spectroscopy to identify biological materials, drugs and pollutants. Mid-IR light can also serve as a carrier of information in free-space optical communications, where data are transmitted through the air without using cables or fibers. Better control of mid-IR light could therefore lead to more sensitive detectors and faster communications.

Metasurfaces are one solution scientists are exploring to achieve this kind of control. These ultrathin structures are built using nanoscale patterns that can shape and direct light waves. Unfortunately, most metasurfaces developed thus far are static: Once fabricated, their optical properties are fixed, limiting their use in real-world photonic systems.

Now, researchers led by Hatice Altug in the Bionanophotonic Systems Laboratory (BIOS) in EPFL’s School of Engineering have overcome this bottleneck with metasurfaces based on suspended membranes of crystalline silicon. By inducing mobile electrical charges within the silicon itself, the researchers can change how the metasurfaces respond to light in real time without changing their physical structure. The devices also achieve record optical performance, with more than an order of magnitude better performance in key metrics compared with previous mid-IR platforms based on similar materials.