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Researchers Develop Mini Flexible Lenses with Wide Field of View

09 November 2015

Researchers from the University of Wisconsin-Madison (UW-Madison) have created miniature lenses with vast range of vision inspired by insects’ multi-faceted eyes. What they created is the first-ever flexible Fresnel zone plate microlenses with a wide field of view that could impact a variety of fields and electronics such as surgical scopes and security cameras by capturing a broader perspective at a fraction of the size required by conventional lenses.

The team, led by Hongrui Jiang, professor of electrical and computer engineering at UW-Madison, designed the lenses no larger than a pin head 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.

Since they used Fresnel zone plates, the researchers can freely reconfigure the shape of the lens array too.

Tiny silicon nano-wire towers make up dark regions of the flexible Fresnel zone lenses. Image Credit: Hongrui JiangTiny silicon nano-wire towers make up dark regions of the flexible Fresnel zone lenses. Image Credit: Hongrui JiangConventional lenses use refraction in order to focus on a single point, but the zone plates focus by diffraction—bending light as it passes the edge of a barrier.

Each of the half-millimeter diameter lenses resembles a series of ripples on water. 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.

When other groups have tried to develop Fresnel zone plate lenses, the result was fuzzy vision.

"The dark areas must be very dark," says Jiang. "Essentially, it has to absorb the light completely. It's hard to find a material that doesn't reflect or transmit at all."

To overcome the fuzzy vision obstacle, the team used black silicon to trap light inside the dark regions of their Fresnel zone plate lenses. Black silicon consists of clusters of microscopic vertical pillars, or nanowires, so incoming light bouncing between individual silicon nanowires cannot escape the structure and makes the material darker.

According to the news release:

The team put aluminum rings on top of solid silicon wafers, and etched silicon nanowires in the areas between aluminum rings. Then they seeped a polymer between the silicon nanowire pillars. After the plastic support solidified, they etched away the silicon backing, leaving bull's-eye patterned black silicon embedded in supple plastic.

By doing this, the lenses had crisp focusing capabilities and the flexibility to capture a large field of view.

The researchers are now trying to integrate the lenses into existing optical detectors and directly incorporate silicon electronic components into the lenses themselves.

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