Photonic space-time crystals represent advanced materials that can enhance the effectiveness and efficiency of wireless communication and laser systems. These materials display a repetitive structure in three dimensions and also in time, allowing for meticulous control over light’s characteristics. A team of scientists from the Karlsruhe Institute of Technology (KIT), in collaboration with Aalto University, the University of Eastern Finland, and Harbin Engineering University in China, has demonstrated practical applications for these four-dimensional materials. Their findings were published in Nature Photonics.
Photonic time crystals are substances with a consistent composition in space, yet their properties change periodically over time. This temporal variation helps in modulating and amplifying the spectral characteristics of light, essential for optical information processing. Professor Carsten Rockstuhl, from KIT’s Institute for Theoretical Solid-State Physics and Institute of Nanotechnology, noted, “This presents us with new opportunities but also significant challenges.” He stated that this research opens the door to utilizing these materials in information processing systems that can utilize and enhance light across various frequencies.
A Step Closer to Four-dimensional Photonic Crystals
The crucial feature of a photonic time crystal is its momentum space bandgap. Momentum describes the direction in which light travels. A bandgap indicates the direction light must take for amplification, with a wider bandgap allowing for greater amplification. Puneet Garg, one of the study’s lead authors, explained, “In the past, we needed to enhance the periodic changes in material properties, such as the refractive index, to achieve a wide bandgap. Only then could light be amplified at all. However, most materials offer limited options for this, which presents a considerable challenge.”
The researchers found a solution by merging photonic time crystals with an additional spatial structure. They developed “photonic space-time crystals” by combining photonic time crystals made of silicon spheres, enabling them to “trap” light longer than was previously feasible. This prolonged interaction allows light to respond more effectively to the periodic alterations in material properties. “We’re talking about resonances that enhance the interactions between light and matter,” remarked Xuchen Wang, the other lead author. “In such finely tuned systems, the bandgap nearly spans the entire momentum space, allowing light to be amplified regardless of its propagation direction. This could be a pivotal breakthrough for the practical application of these innovative optical materials.”
“We’re thrilled about this advancement in photonic materials and are eager to observe the long-term effects of our research. Now, the tremendous potential of contemporary optical materials research can come to fruition,” Rockstuhl commented. “This concept isn’t confined to optics and photonics; it has potential applications in numerous physical systems and could spark new research across various domains.”
This research was conducted under the “Wave phenomena: analysis and numerics” Collaborative Research Center, which is supported by the German Research Foundation (DFG) and is part of the Helmholtz Association’s Information research field.
