A new theoretical framework has been proposed that enables directional control of light scattering even in disordered structures.
A research team led by Professors Sunkyu Yu and Namkyoo Park of the Department of Electrical and Computer Engineering at Seoul National University College of Engineering, in collaboration with Professor Xianji Piao of the University of Seoul, has developed a new theoretical framework that can suppress light scattering in certain directions while enhancing it in others, even in irregularly arranged materials. The work extends research on controlling light scattering, which has traditionally centered on ordered crystal structures, into the realm of disordered systems.
Scattering—the process by which light is dispersed in multiple directions when it encounters matter—plays a critical role in determining the performance of a wide range of optical technologies, including anti-reflective coatings for eyeglasses and camera lenses, display diffusers, LiDAR sensors for autonomous vehicles, and optical communication components. Ultimately, the ability to precisely control scattering is a key determinant of competitiveness in optical technologies.
The researchers proposed a theory they call “Non-Hermitian Statistical Crystallography,” which considers not only the refractive properties but also absorption and amplification. Based on statistical correlations and rotational symmetries between refractive properties and absorption/amplification properties, the theory provides a conceptual framework for classifying and designing the scattering characteristics of open, disordered materials.
The findings were published on August 6 in the international journal Advanced Science .
Until now, one of the principal approaches to precisely controlling light has been to use crystalline structures in which atoms or microstructures repeat at regular intervals. The researchers, however, turned their attention to hyperuniform structures, which appear irregular at short distances but are distributed uniformly over larger scales. An analogy is an audience at a concert venue: people may appear to be standing randomly when viewed up close, yet if no section is either empty or excessively crowded, the overall density appears uniform from a distance. Similarly, hyperuniform structures are disordered locally but evenly distributed at larger scales. Such structures scatter certain types of light only minimally.
When this suppression of scattering extends across a certain range of wavelengths and directions, a phenomenon known as “stealthy hyperuniformity” emerges. Much like a stealth aircraft leaving almost no reflected signal at certain radar wavelengths, such a material effectively becomes “invisible” to light within specified ranges of wavelengths and directions.
Previous studies of hyperuniformity have primarily focused on materials in which energy is conserved. In real optical systems, however, light can be absorbed or amplified through externally supplied energy. Open wave systems in which energy can enter or leave in this manner are known as non-Hermitian systems. The researchers proposed treating the “loss” and “gain” of light not as problems to be eliminated, but rather as new design variables. In other words, they extended the theory to open systems, in which energy is exchanged with the external environment, thereby establishing a new principle for controlling scattering.
* Non-Hermitian system: An open wave system in which light or energy can be absorbed or escape to the outside, or conversely can be amplified by energy supplied from an external source. In such systems, not only refractive properties but also gain and loss determine wave behavior.
The researchers first identified the conditions required for non-Hermitian hyperuniformity. They demonstrated that when both the refractive properties and the absorption/gain properties independently satisfy hyperuniformity, scattering suppression can be maintained in the long-wavelength regime while desired scattering characteristics can still be tailored.
The team then found that cross-correlation, which describes how refractive properties and absorption/gain properties are spatially arranged relative to one another, is a key factor in determining scattering in specific directions. By controlling this cross-correlation, the researchers were able to design directional scattering that suppresses light in one direction while enhancing it in another. In particular, they demonstrated that it is possible to design scattering patterns with odd-fold rotational symmetry, which are difficult to realize in conventional energy-conserving materials.
*Cross-correlation: A statistical relationship describing how two different material properties are arranged relative to each other in space, in terms of distance and direction. In this study, cross-correlations between refractive properties and absorption/gain properties are used to design the directionality and symmetry of scattering.
The researchers further organized these design principles into a new classification framework called Non-Hermitian Statistical Crystallography. Whereas conventional crystallography has provided a basis for understanding and designing crystal structures through X-ray diffraction patterns, the new framework is significant in that it broadens the range of scattering responses that can be realized in disordered, open materials.
The principles proposed by the research team could eventually be used to design optical devices that suppress unwanted scattering or direct light in desired directions in fields including optical communications and photonic integrated circuits, optical sensors and LiDAR, displays and lighting, and medical optical imaging. In optical communications, the approach could be applied to designing components that reduce unwanted reflections, while in optical sensors for autonomous vehicles, it could help develop technologies that suppress stray light from specific directions. The framework is also expected to contribute to the design of optical devices that are relatively robust to manufacturing imperfections, as well as directional optical sensors.
Professors Sunkyu Yu, Namkyoo Park, and Xianji Piao, who jointly supervised the research, said, “This study connects two research areas—non-Hermitian wave physics and hyperuniform materials—and presents a new framework for designing the directionality and symmetry of scattering even in disordered open materials without periodicity.”
They added, “Going forward, we plan to implement the proposed theory in physical material platforms and extend the research to strong multiple scattering and non-Hermitian band phenomena.”
Co-first authors Gitae Lee and Ikbeom Lee, doctoral researchers, and Seungmok Youn, an undergraduate researcher, said, “It was particularly meaningful to develop a statistical understanding of scattering in disordered structures within open systems where energy is exchanged with the external environment, and to use this understanding to propose a new framework for classifying the scattering properties of open materials.”
They added, “We hope these findings will contribute to future research on non-Hermitian disordered systems.”
The study was conducted with Gitae Lee, Ikbeom Lee, and Seungmok Youn serving as co-first authors and leading the development of the theoretical framework, microstructure design, and numerical analysis. Doctoral researchers Gitae Lee and Ikbeom Lee are conducting research on disordered wave optics at Seoul National University’s Intelligent Wave Systems Laboratory. Seungmok Youn plans to continue research on photonic integrated circuits at Harvard University.
The research was supported by the National Research Foundation of Korea (NRF) through the Basic Research Laboratory (No. RS-2024-00397664), Innovation Research Center (No. RS-2024-00413957), Young Researcher Program (No. RS-2025-00552989), Core Research Grants (No. RS-2026-25469085), and Midcareer Researcher Program (No. RS-2023-00274348), all funded by the Korean government. The research was also supported by the BK21 FOUR program of the Education and Research Program for Future ICT Pioneers in 2026, through Seoul National University.
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Advanced Science
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The authors declare no conflicts of interest.