Researchers in Germany develop novel optical diffuser, based on silicon nanoparticles

23 Dec 2021

Device can control the direction, wavelength and polarization of light, for transparent screens or AR applications.

Miniaturization of optical components is a challenge in photonics. Researchers at Karlsruhe Institute of Technology (KIT) and Friedrich Schiller University of Jena have succeeded in developing a diffuser, a disk that scatters light, based on silicon nanoparticles.

The device can be used to specifically control the direction, color, and polarization of light. This novel technology may be used in transparent screens or augmented reality, say its developers.

The work is described in Advanced Materials.

Diffusers are disks that scatter incident light in all directions with the help of small scattering centers. To overcome the bulkiness of conventional optical diffusers, researchers the KIT and Friedrich Schiller team applied a layer of specially-designed silicon nanoparticles onto a substrate and arranged the particles in a disordered, but carefully planned manner.

The nanoparticles interact with certain, adjustable wavelengths of light. The direction, color, and polarization of light can be controlled specifically with these metasurfaces.

‘Sweet spot’ for perfect diffusion

The team of researchers faced two fundamental questions, as explained by Aso Rahimzadegan, doctoral researcher of KIT and one of the two main authors of the study: “To what an extent can we make the optical diffuser smaller and what must the disorder in the arrangement of the nanoparticles be like?”

Dennis Arslan, a doctoral researcher at Jena University and second main author, explained: “Remarkably, we found a sweet spot for the amount of disorder that leads to perfect diffusion. We fabricated metasurface diffusers that appear to be equally bright from all directions when looked at with the naked eye. The remarkable aspect is that this happens in a layer that is 0.2 micrometers in thickness only. The diffusers scatter light of a specific color and let other wavelengths pass undisturbed.”

Such property is useful in scientific applications, but also consumer devices, such as transparent screens that can be viewed from both sides, holographic projectors, or augmented reality headsets profit from it. Combination of experimental and theoretical expertise from both partners made it possible to provide answers to these challenging scientific questions.

Research that led to these results was carried out under the “Tailored Disorder” priority program funded by the German Research Foundation. At KIT, this work was part of the 3D Matter Made to Order Cluster of Excellence.