This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Augmented reality (AR) glasses, lenses thinner than a human hair, and holograms floating above your fingertips may sound like technologies from science fiction. At the heart of these emerging technologies, however, lies a nanoscale optical device known as a "metasurface." Made of nanostructures smaller than the wavelength of light, metasurfaces can precisely control the direction, color and other properties of light.
Despite their remarkable capabilities, their complex structures have long posed a major challenge to researchers. A research team led by Professor Junsuk Rho and Dr. Seokwoo Kim of POSTECH discovered hidden repeating patterns within seemingly disordered nanostructures, opening a new route toward faster and more accurate analysis and design of metasurfaces.
The study was published in Nature Communications. To achieve a desired optical function, metasurfaces are designed by gradually varying the size, shape or orientation of individual nanostructures. As these structures become increasingly different from one another, however, the periodicity of the overall surface is lost, making it difficult to calculate how the device interacts with light.
If a structure is periodic, researchers can analyze only a small portion of it and predict the behavior of the entire device. In contrast, an aperiodic structure may require an enormous number of individual nanostructures to be calculated separately. A metasurface measuring several centimeters across can contain more than 1 billion nanostructures, making rigorous computer simulations extremely time-consuming.
Conventional approaches have therefore often relied either on simplified assumptions or on computationally demanding large-scale simulations. The research team focused on the idea that even a structure that appears highly complex may contain an underlying repeating order. They found a clue in the Moiré pattern, a large-scale interference pattern that appears when two regular patterns with slightly different alignments or spacings are overlaid.
A familiar example can be seen when two layers of mosquito netting or thin curtains are placed on top of each other. The researchers interpreted the basic lattice of a metasurface and the additional spatial variation introduced to redirect light as two overlapping patterns. They then mathematically demonstrated that when the orientation and spacing of these patterns satisfy specific conditions, a large-scale repeating pattern emerges even within a structure that initially appears aperiodic.
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