UC Berkeley scientists, using an insect eye as a prototype, have created an artificial compound eye that one day might make it to endoscopes, laparoscopes and other equipment. According to UC Berkeley, such an artificial eye system will allow a “wider field of vision than previously possible, even with the best fish-eye lens”:
They are the first hemispherical, three-dimensional optical systems to integrate microlens arrays – thousands of tiny lenses packed side by side – with self-aligned, self-written waveguides, that is, light-conducting channels that themselves have been created by beams of light, said Lee, the Lloyd Distinguished Professor of Bioengineering at UC Berkeley.
The eyes are fully described for the first time in the April 28 issue of the journal Science.
“I’ve always wanted to create an advanced, three-dimensional optical system,” Lee said, “but conventional microfabrication technology is two-dimensional. So, I started thinking about basing a fabrication system on the developmental stages of insect eyes that I’d learned about as a biophysicist and bioengineer.”
What he and his team came up with is a low-cost, easy-to-replicate method of creating pinhead-sized polymer resin domes spiked with thousands of light-guiding channels, each topped with its own lens. Not only are these units packed together in the same hexagonal, honeycomb pattern as in an insect’s compound eye, but each is also remarkably similar in size, design, shape and function to an ommatidium, the individual sensory unit of a compound eye.
While conventional microfabrication techniques are expensive and use high temperatures, Lee and his team borrowed from nature, using a low temperature system, photopolymerization, and self-aligning, self-writing technology.
To create the artificial eye, the team first needed to construct a hemispherical mold of the eye’s outer layer, a structure consisting of thousands of microlenses. Using existing technology, they made a flat array of these tiny, domed lenses arranged in the hexagonal honeycomb pattern. On top of this, they applied a thin slab of an elastic polymer called polydimethylsiloxane, or PDMS, creating a concave pattern of the lenses in the polymer. By affixing the PDMS membrane over the opening of a vacuum chamber and applying negative air pressure, they pulled it into the dome shapes they needed, controlling its form by using different pressures.
They then had a hemisphere-shaped cup pocked with some 8,700 indentations: a compound-eye mold that could be used over and over again using soft lithography technology, a set of methods developed over the last decade to replicate nanoscale-sized structures.
The material they chose for the artificial eyes was an epoxy resin that cures into a hardened form when exposed to ultraviolet light. They poured the resin into the dimpled molds, baked it at a low temperature just long enough to slightly harden the material, then turned out the contents: little resin hemispheres with a surface packed with 8,700 raised mounds. When struck by a beam of light, each of these mounds acts as a lens, focusing the light and sending it into the material below. Like a welder’s torch burning a hole into metal, over time the focused light beams etch holes in the resin creating the tiny channels called self-written waveguides.
Because these channels are formed at the angle of the light beams that strike them, Lee used a condenser lens to bend his light source into a spoke-like pattern of beams that converges on the eye’s dome. The end result is that the waveguides pierce the resin at angles that head toward the center of the dome, just like the converging ommatidia of an insect eye.
Because the microlenses create the waveguides, each microlens is perfectly aligned with its waveguide. The self-alignment, self-writing processes are crucial to the creation of the artificial compound eye, said Lee, because these processes will also align the microlenses and waveguides with the pixels of CCDs and spectroscopes.
The press release…
The BioPOETS (Biomolecular Polymer Opto-Electronic Technology and Science) group website…
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