Theoretical framework expands directional light control beyond ordered crystal structures

Researchers at Seoul National University College of Engineering have developed a new theoretical framework that can manipulate light scattering in disordered materials, expanding the control beyond traditional ordered crystal structures. This innovation, called "Non-Hermitian Statistical Crystallography," enables suppression of light scattering in specific directions while enhancing it in others, even in irregularly arranged materials.

Scattering of light by matter influences the performance of various optical technologies such as anti-reflective coatings, display diffusers, LiDAR sensors, and optical communication components. Controlling scattering is thus crucial for the competitiveness of these technologies. The researchers, led by Professors Sunkyu Yu and Namkyoo Park, and Professor Xianji Piao, propose a theory that considers the refractive properties and absorption/amplification of materials, rather than just their crystallographic arrangements.

The framework, built on statistical correlations and rotational symmetries between these properties, categorizes and designs scattering characteristics of open, disordered materials. Hyperuniform structures, which appear irregular at short distances but are uniformly distributed over larger scales, were found to scatter certain types of light minimally, leading to a phenomenon known as "stealthy hyperuniformity."

This can make materials "invisible" to light in specific wavelengths and directions, similar to stealth aircraft remaining hidden from radar.

The researchers extended the theory to non-Hermitian systems, where light can be absorbed or amplified externally. By treating light's loss and gain as design variables, they found that non-Hermitian hyperuniformity can maintain scattering suppression in the long-wavelength regime while allowing tailored scattering characteristics.

Controlling cross-correlation between refractive properties and absorption/amplification properties further enabled directional scattering that suppresses light in one direction while enhancing it in another.

This discovery could revolutionize optical devices in various fields, including optical communications, photonic integrated circuits, optical sensors, LiDAR, displays, lighting, and medical imaging. The theoretical framework not only broadens the range of scattering responses achievable in disordered materials but also offers robustness to manufacturing imperfections and potential applications in developing directional optical sensors.