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

Photonics, the science of generating, spreading, and detecting light, is considered the major driver in developing techno­logies for the 21^st century. The challenge consists in miniatu­rizing conventional optical elements, such as lenses, mirrors, prisms, or diffusers, and enhancing their perfor­mance with features only accessible in the realm of nano­photonics. This leads to new applications, such as minia­turized sensors in autonomous vehicles or integrated photonic quantum computers. 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, the researchers applied a layer of speci­fically designed silicon nano­particles to a substrate and arranged the particles in a disordered, but carefully planned manner. These nanoparticles are a hundred times thinner than a human hair and interact with certain, adjustable wavelengths of light. The direction, color, and polarization of light can be controlled speci­fically with these meta­surfaces.

The team of researchers faced two funda­mental questions: “To what an extent can we make the optical diffuser smaller and what must the disorder in the arrangement of the nano­particles be like?,” says Aso Rahim­zadegan, doctoral researcher of KIT. “Remarkably, we found a sweet spot for the amount of disorder that leads to perfect diffusion.“ Dennis Arslan, doctoral researcher at Univer­sity of Jena, explains: “We fabri­cated meta­surface diffusers which appeared 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. (Source: KIT / U. Jena)

Reference: D. Arslan et al.: Toward Perfect Optical Diffusers: Dielectric Huygens’ Metasurfaces with Critical Positional Disorder, Adv. Mat., online 13 October 2021; DOI: 10.1002/adma.202105868

Link: Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Jena, Germany • Karlsruhe School of Optics and Photonics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany