Daylight window based on the nano-disorder inspired by Morpho butterflies’ coloration

Abstract

Some species of Morpho butterflies reflect interfered brilliant blue, which is contradictory to the interference effect due to low angular dependence. This coloration is typically attributed to the disordered nanostructure of the species scales. Applying this reflective principle into light transmission, we discover a new daylight window with high transmittance, wide angular spread, and low color dispersion. The effectiveness of this window was verified through numerical simulations. The optical conditions were investigated by changing the structural parameters, and the required conditions were clarified. This concept realizes an ideal window based on a new principle.

Development of a High‐Performance, Anti‐Fouling Optical Diffuser Inspired by Morpho Butterfly's Nanostructure

“…Inspired by this light‐diffusing mechanism, we proposed Morpho ‐type diffusers, in which randomly arranged nanopillars diffract the transmitted light waves into a wide angular range without forming gratings (Figure 1c). [ 42 ] Here, the multilayered structures that cause strong light reflection were removed to enable the majority of incident light to pass through the nanostructures without multiple scattering. Consequently, the same diffusing principles would work for the transmitted light, resulting in i) high transmittance, ii) wide‐angle diffusion, and iii) low dispersion.…”

“…This is because the phase difference among the diffracted waves is smaller in transmission mode as compared with reflection, and accordingly the vertical randomness (height deviation) of nanostructures must be large enough to generate sufficient phase variation for anti‐grating. [ 42 ]…”

“…The feasibility of protective layers also has significant implications in applications. For example, daylight harvesting windows [ 42 ] that diffuse the incident sunlight to utilize it for indoor lighting, can be realized by only attaching our diffuser to a glass window without any additional construction. In addition, conventional surface‐relief diffusers generally require careful handling and allow limited applications such as optical elements, because they do not incorporate surface protection.…”

“…This type of diffuser ( Morpho ‐type diffuser) was shown to fulfill i) high transmittance of 90%, ii) wide‐angle diffusion (FWHM ≈ 90°), and iii) low dispersion in two‐dimensional (2‐D) optical simulations. [ 42 ] We previously demonstrated a Morpho ‐type diffuser with optical performance similar to the simulation model (transmittance = 85%, FWHM ≈ 70°, and low dispersion) using nanoimprint lithography. [ 43 ] However, the optical performance of this prototype was incomplete at two points: the surface nanopattern was designed with random‐sized rectangles forming a checkered pattern, which produced intense crossed lines in the diffraction pattern and impaired the spatial uniformity of light diffusion; the controllability of anisotropy was not attained as only an anisotropic diffusion was demonstrated.…”

“…This is because the phase difference among the diffracted waves is smaller in transmission mode as compared with reflection, and accordingly the vertical randomness (height deviation) of nanostructures must be large enough to generate sufficient phase variation for anti-grating. [42] However, the nanostructures shown in Figure 1c are extremely difficult to realize as the surface comprises randomly distributed nanopillars with high aspect ratios. Therefore, the hierarchical design was simplified into 2-D (in-plane) structures to enable practical fabrication by nanoimprint lithography.…”