An efficient optical diffuser fabricated from fungal mycelium

Abstract

Scattering of light from randomly textured materials is ubiquitous and of great interest in biology and for diverse applications—including filtering, light trapping in solar cells, and speckle photography. One attractive means to build these materials is by harnessing the complexity present in structures of biological origin. Here, we report on the development of a random phase diffuser based on intertwined filamentous cells (hyphae) of the fungus Trichoderma atroviride. A fungal colony (mycelium) is grown on the surface of a gel medium, and then removed, fixated, and dehydrated, resulting in a free-standing, two-dimensional random mesh (1 cm × 1 cm × 5 μm) composed of rigid hyphae separated by air gaps. A laser beam incident on the bioplate results in speckle patterns of nearly equal intensity in transmission and reflection. By modeling the bioplate as composed of optical phase elements and computing Fraunhofer diffraction, we recover the overall shape of the observed diffuse light spot. As the hyphal density composing the sample is increased, all optical power is in the speckle pattern, and approximate Lambertian transmissivity is reached. Altogether, our observations suggest that a planar fungal colony can scatter light efficiently by imparting a random phase. These results underscore the potential of a biological structure to develop optical elements and to use light scattering to evaluate morphology in complex structures—such as filamentous mycelia.