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Butterflies, MEMS, and Displays
Isao Shimoyama, Professor, Department of Mechano-Informatics,
Graduate School of Information Science and Technology, the University of Tokyo
It seems that printed materials and computer displays havebecome very colorful these days. In my school days and when I
join the faculty, I remember that the computer displays weremonochrome CRT monitors that displayed green text on a black
background, and the more expensive displays depicted green
graphics with electron beams. Then before I knew it, thesemonitors had been replaced by LCD monitors in high-resolution
color. In the days leading up to this years Olympics, electronic
shops in Akihabara and Shinjuku have been overflowing withlarge displays projecting beautiful pictures. I believe displays
will further evolve toward three-dimensional stereoscopic
images in more realistic colors.
It should be possible to produce devices with high added
value using MEMS to implement functions expressed innanoregions. While carbon nanotubes and quantum dots haveattracted much attention as devices used on a nanoscale, lightinterference is a phenomenon that involves wavelengths oflight, which are on the order of submicrons. Accordingly, wecould call light interference a function manifested on ananoscale. While carbon nanotubes and quantum dots haverecently been created artificially, objects in which thephenomenon of light interference can be observed have existed
in the natural world since long ago.
These photos taken by Eiji Iwase depict a Morpho butterfly
and its scales. A Morpho butterfly does not produce colors
through pigmentation in its wings. Rather, light is reflected anddiffracted by minute three-dimensional structures in thesurfaces of the scales and appears to our eyes as beautiful
colors through light interference. The wavelengths of light thatcan be seen through interference depend on the surface
structure. Hence, the colors can be changed by changing thestructure of the surface. Changing microstructures of a surface
is a specialty of MEMS to achieve an effect considerably
different from the fixed light wavelengths produced from LED
illumination and pigments.
Humans have photoreceptor cells corresponding to the RGB(red, green, and blue) colors. When light enters the human eye,these photoreceptor cells read wavelengths of the RGB
components and see combinations of the component
magnitudes as colors. However, the photoreceptor cells ofinsects are different from those of humans, possessing asensitivity to light having wavelengths different from the RGB
wavelengths. In other words, insects apparently receive
different visual stimuli from that received by humanphotoreceptor cells when humans view nature. In previous
discussions with researchers who observe the behavior ofinsects while shining lights on their visual systems, they asked
me if it would be impossible to create an LCD panel that could
be used to visually stimulate insects. Certainly our liquid crystal
displays use only RGB components, which cannot stimulate
photoreceptor cells sensitive to UV rays.
While LCD monitors depict colors by combining illuminationand intensities of the three primary colors of light, the colors
obtained from this display represent only a portion of the colors
in nature. In other words, these representations are missing
data for light of wavelengths other than the three primarycolors and data of light spectrums dependent on the directionof light reflection. Therefore, while light produced by these
displays appears somewhat natural to humans, it cannot be said
to reproduce nature.
Enter MEMS. If MEMS can be used to freely adjust thespectrum of light rays emitted into space at each point of thedisplay, it should be possible to reproduce sensations of lightdependent on the positions of the light sources, objects, and theeye, such as a silver-like metallic luster. MEMS are also effective

for incorporating light-emitting elements having wavelengths
other than RGB in displays.
So how, specifically, can we implement these ideas? I heardthat a mathematician once said, "I have proved it, but there is
not enough space to write it down." In the same way, I would
like to say that I have an idea, but there is not enough space inthis paper to explain.

Photo 1 The Morpho butterfly

Photo 2 An enlarged view of the wing scales

Photo 3 A cross-sectional view of the scales further
enlarged; the microstructure of the scales
produces beautiful colors through lightreflection, diffraction, and interference4