Interactions between light and matter can be exploited better with photonic space-time crystals. Credit: Xuchen Wang / Aalto University
Photonic space-time crystals enhance light interaction and amplification, offering new applications in optical information processing.
Photonic space-time crystals are advanced materials designed to enhance the performance and efficiency of technologies like wireless communication and lasers. These crystals have a unique structure that is periodically arranged in three spatial dimensions and also changes over time, allowing precise control of light’s behavior. Researchers from the Karlsruhe Institute of Technology (KIT), in collaboration with Aalto University, the University of Eastern Finland, and Harbin Engineering University in China, have demonstrated how these four-dimensional materials can be applied in real-world technologies. Their findings were published in Nature Photonics.
Photonic Time Crystals
Photonic time crystals are materials with a consistent structure in space but properties that change periodically over time. This time-based variation allows light’s spectral composition to be modulated and amplified, making them valuable for optical information processing.
“This gives us new degrees of freedom but also poses a lot of challenges,” explained Professor Carsten Rockstuhl from KIT’s Institute for Theoretical Solid-State Physics and Institute of Nanotechnology. “This study paves the way for using these materials in information processing systems capable of using and amplifying light of any frequency.”
A Step Closer to Four-dimensional Photonic Crystals
The key parameter of a photonic time crystal is its bandgap in momentum space. Momentum is a measure of the direction in which light propagates. A bandgap specifies the direction in which light has to propagate in order to be amplified; the wider the bandgap, the greater the amplification.
“Previously we’ve had to intensify the periodic variation of material properties such as the refractive index to achieve a wide bandgap. Only then can light be amplified at all,” explained Puneet Garg, one of the study’s two lead authors. “Since the options for doing that are limited for most materials, it’s a big challenge.”
Advancing Optical Materials with Space-Time Crystals
The researchers’ solution involved combining photonic time crystals with an additional spatial structure. They created “photonic space-time crystals” by integrating photonic time crystals made of silicon spheres that “trap” and hold light longer than had previously been possible. The light then reacts much better to periodic changes in material properties.
“We’re talking about resonances that intensify the interactions between light and matter,” said Xuchen Wang, the other lead author. “In such optimally tuned systems, the bandgap extends across nearly the entire momentum space, which means light can be amplified regardless of its direction of propagation. This could be the crucial missing step on the way toward practical use of such novel optical materials.”
Potential and Applications of Photonic Innovations
“We’re very excited about this breakthrough in photonic materials, and we look forward to seeing the long-term impact of our research. Now the enormous potential of modern optical materials research can be realized,” Rockstuhl said. “The idea isn’t limited to optics and photonics; it can be applied to various physical systems and has the potential to inspire new research in other fields.”
Reference: “Expanding momentum bandgaps in photonic time crystals through resonances” by X. Wang, P. Garg, M. S. Mirmoosa, A. G. Lamprianidis, C. Rockstuhl and V. S. Asadchy, 12 November 2024, Nature Photonics.
DOI: 10.1038/s41566-024-01563-3
This research project was carried out in the “Wave phenomena: analysis and numerics” Collaborative Research Center, funded by the German Research Foundation (DFG), and is embedded in the Helmholtz Association’s Information research field.
