Light diffusor inspired by morpho butterflies with bright, wide angled light, and no polarization created by Osaka University

Light-diffusing materials that have been used to date have either diffused light by embedding micro-scatterers or bent light via refraction due to micro-irregularities present on the surface. However, with conventional scatterers, 'brightness' and 'angular spread' are incompatible and there are drawbacks such as insufficient angular spread and easy contamination with refractors.

A research group led by Associate Professor Akira Saito and Graduate Student Kazuma Yamashita of the Graduate School of Engineering at Osaka University has developed the world's first nanostructured light-diffusing architecture with standard fabrication tools. This sheet is bright, wide-angled, color-balanced, and stain-resistant. Furthermore, it can control the anisotropy of diffuse light. By analyzing the wings of morpho butterflies, which have bright, wide-angle, and unbiased color reflections and are water repellent, and applying them to transmissions, the research group was able to create a remarkable innovation. The results were published in the journal Advanced Optical Materials.

The research group has fabricated a light-diffusing sheet utilizing diffraction from nanostructures. They harnessed the unique microstructure of morpho butterflies, which diffracts light from a narrow width to spread it over a wide angle and prevent color bias caused by clutter. Because diffraction occurs only at the surface, high transmittance is also achieved. The nano-unevenness of the surface has an anti-fouling function, which is a result of the same effect responsible for the water-repellent nature (known as the lotus effect) of lotus leaves.

The structure was developed by electromagnetic field simulation to enable actual fabrication. Actual fabrication using semiconductor technology demonstrated that this structure fulfilled the required criteria, namely selective reflection over a ±40°from the direction of illumination, a transmittance of ~90%, no color dispersion, and anti-fouling functionality. Depending on the design, the shape anisotropy of diffuse light can also be controlled. This technology is expected to find applications in lighting windows for energy conservation and light-diffusing sheets for various types of lighting and displays.

Saito commented, "Organisms are a treasure trove of excellent features. This sheet was initially theoretically validated as daylight-harvesting window two years ago. Following a year of prototyping and refinement, all its intended functions have now been realized and demonstrated. While additional work is required to reduce costs and enable production of larger-sized sheets, the potential applications of the sheet, including architecture and lighting, are also attractive."

Journal Information
Publication: Advanced Optical Materials
Title: Development of a High-Performance, Anti-Fouling Optical Diffuser Inspired by Morpho Butterfly's Nanostructure
DOI: 10.1002/adom.202301086