(November 4, 2015) Drawing
inspiration from an insect's multi-faceted eye, University of Wisconsin-Madison
engineers have created miniature lenses with vast range of vision.
Their new approach created the first-ever flexible Fresnel
zone plate microlenses with a wide field of view - a development that could
allow everything from surgical scopes to security cameras to capture a broader
perspective at a fraction of the size required by conventional lenses.
Led by Hongrui Jiang, professor of electrical and computer
engineering at UW-Madison, the researchers designed lenses no larger than the
head of a pin and embedded them within flexible plastic. An array of the
miniature lenses rolled into a cylinder can capture a panorama image covering a
170-degree field of view.
"We got the idea from compound eyes," says Jiang,
whose work was published in the Oct. 30 issue of the journal Scientific
Reports. "We know that multiple lenses on a domed structure give a large
field of view."
And the researchers can freely reconfigure the shape of the
lens array, because rather than relying on conventional optics for focusing,
they used Fresnel zone plates.
Conventional lenses use refraction - the way light changes
direction while passing through different substances (typically stiff, translucent
ones, like glass) - to focus it on a single point. Named for 19th century
engineer Augustin-Jean Fresnel, the zone plates focus by diffraction - bending
light as it passes the edge of a barrier.
Each of Jiang's half-millimeter diameter lenses resembles a
series of ripples on water emanating out from the splash of a stone. In
bull's-eye fashion, each concentric ring alternates between bright and dark.
The distance between the rings determines the optical properties of the lens,
and the researchers can tune those properties in a single lens by stretching
and flexing it.
Previous attempts at creating Fresnel zone plate lenses have
suffered from fuzzy vision.
"The dark areas must be very dark," explains
Jiang, whose work is funded by the National Institutes of Health.
"Essentially, it has to absorb the light completely. It's hard to find a
material that doesn't reflect or transmit at all."