Apply a little ultraviolet light and heat, and a gumdrop of polymer transforms itself into an artificial bug eye, biophysicists report. The advance could lead to small, inexpensive wide-angle cameras for surveillance, biomedical imaging, and other applications.
Optically speaking, it's hard to take a broad view of things. To produce lenses with fields of view wider than 90°, lens makers must combine several individual lenses in an elaborate "fish eye" structure that is expensive and hard to miniaturize. Alternatively, they might try to capture a panoramic view by assembling many smaller "microlenses" pointing in different directions, like the elements in an insect's compound eye. Researchers have developed microlens arrays on light-sensitive microchips. But those devices have been flat, which limits their field of view. And researchers must align the optics with the light-detecting pixels on the chip.
Now, biophysicist Luke Lee and colleagues at the University of California, Berkeley, have produced a 3-dimensional artificial compound eye that neatly cobbles itself together. To begin, the researchers created a series of dimples in a hexagonal pattern on a circular sheet of flexible polymer. They then stretched the sheet over a hole in the wall of a small vacuum chamber and sucked out the air to bow the sheet into a hemisphere. Finally, the team used the deformed sheet to mold a gumdrop-like dome of light-sensitive polymer covered with bulges that acted like lenses.
Lee and colleagues illuminated the dome from all sides with ultraviolet light. Each 25-micrometer-wide microlens focused the light and beamed it through the polymer below. The light caused a chemical reaction in the polymer that changed its "index of refraction" along the path of the beam, thus creating a pipelike light-guide from the lens to a spot on the back of the gumdrop, where the light could feed into a pixel on a chip. Because the lens created the beam, the lens and light-guide automatically lined up. Finally, the researchers heated the 2.5-millimeter-wide dome to set the rest of the polymer.
In tests, the artificial eye performed much like a bee's eye, with each microlens capturing light from a field of view 4° or smaller and with roughly the same efficiency. It might be used to make small security cameras or endoscopes, says Lee, whose team reports its work in tomorrow's issue of Science.
"The strength of this approach is the reproducibility, which is very important if you want to look at applications," says Eduardo Charbon, an electrical engineer at the École Polytechnique Fédérale de Lausanne in Switzerland. Unlike some clever ideas, Charbon says, the artificial eye should be fairly easy to manufacture and turn into a practical technology.
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