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Fresnel Microlenses Developed for Superior Field of View at Small Sizes

Category: Science & Technology
Posted: 06:21AM

Lenses can be a big deal, both when it comes to their influence on images and their physical size. This is because traditional lenses use refraction to affect light and require more of a material to affect light more. Fresnel zone plate lenses, however, rely on diffraction and can be very thin, as researchers at the University of Wisconsin, Madison have demonstrated.

Diffraction concerns how light bends when it pass a barrier's edge, and Fresnel lenses take advantage of it by selectively bending the light to focus it like a conventional lens. To achieve this, the lenses consist of concentric rings alternating between light and dark areas. If the dark areas are not dark enough though, the image will be fuzzy. To overcome this problem, the researchers used black silicon, which traps light in a forest of nanowires. They made the lens by patterning aluminum rings onto silicon wafers and then etching the nanowires into the wafer, creating the black silicon rings. Finally a plastic support was applied and the remaining unwanted silicon was etched away, leaving the Fresnel lens in a flexible plastic.

Because Fresnel zone plate lenses can be made so much thinner and smaller than conventional lenses, potential applications include lenses on surgical scopes that can see more without being too large. By rolling an array of these lenses into a cylinder, they can capture an image with a 170º field of view.

Source: University of Wisconsin, Madison

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