Coming soon: A camera based on the human eye

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London, Aug 7 : Digital cameras would soon be more humanised, what with a new technology that can produce images with a wider field of view, just like the human eye.

In a collaborative study, Yonggang Huang, Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering and John Rogers, the Flory-Founder Chair Professor of Materials Science and Engineering have created array of silicon detectors and electronics that can be conformed to a curved surface.

Thus, just like the human eye, the curved surface can act as the focal plane array of the camera, which captures an image.

In a normal camera, such electronics must lie on a straight surface, and the camera's complex system of lenses have to reflect an image several times before it can reflect on the right spots on the focal plane.

"The advantages of curved detector surface imaging have been understood by optics designers for a long time, and by biologists for an even longer time. That's how the human eye works -- using the curved surface at the back of the eye to capture an image," Nature quoted Huang, as saying.

The researchers established experimental methods and theoretical foundations for an effective way to transfer the electronics from a flat surface to a curved one.

They created a hemispherical transfer element made out of a thin elastomeric membrane that can be stretched out into the shape of a flat drumhead. In this form, planar (flat) electronics can be transferred onto the elastomer. Popping the elastomer back into its hemispheric form enables the transfer of the electronics onto a hemispherical device substrate.

But the drawback was that such a process applied to conventional electronics leads to catastrophic mechanical fracture in the brittle semiconductor materials

Thus they created an array of photodetectors and circuit elements that are so small -- approximately 100 micrometers square -- they aren't as affected when the elastomer pops back into its hemispheric shape.

In addition, each of these devices on the array is connected by thin metal wires on plastic, which form arc-shaped structures that Huang and Rogers call "pop-up bridges." These bridges interconnect the silicon devices, thereby relaxing all of the strain associated with return of the elastomer to its curved shape.

The array was also designed in such a way that the silicon component of each device is sandwiched in the middle of two other layers, the so-called natural mechanical plane. That way, while the top layer is stretched and the bottom layer is compressed, the middle layer experiences very small stress.

The images obtained using this curved array in an electronic eye-type camera indicate large-scale pictures that are much clearer than those obtained with similar, but planar, cameras, when simple imaging optics are used.

"In a conventional, planar camera, parts of the images that fall at the edges of the fields of view are typically not imaged well using simple optics. The hemisphere layout of the electronic eye eliminates this and other limitations, thereby providing improved imaging characteristics," said Huang.

The results of this research will be published as the cover story in the upcoming issue of the journal Nature.


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