Researchers have announced a technological development they say will improve the functionality of digital cameras and other imaging products. Yonggang Huang, a professor at Northwestern University, and John Rogers of the University of Illinois at Urbana-Champaign have created a lens they said was inspired by the human eye.
In addition to enhancing digital camera technology, the eye-shaped lens could have an impact on many devices, Huang said.
“Camera technologies can benefit directly from these advances. We believe, more generally, that many new application possibilities will emerge from the ability to integrate … optoelectronic devices onto curved surfaces. Bring electronics to the human body in the form of advanced biomedical devices is one broad area of possible application,” he told TechNewsWorld.
Before the technology can be used in something like an optical prosthetic, however, other issues must also be resolved.
“We would like to explore the ability of these types of approaches for implantation into the human eye, for people who suffer from degeneration of the retina. Many other problems, mainly in the area of biocompatibility and bio-interfaces would need to be solved first, however,” Huang added.
The two researchers spent two years investigating ways to develop approaches that would bypass the planar, 2-D constraints typically associated with conventional CCD (charge-coupled device) cameras, thereby enabling designs inspired by the human eye.
The result of their research is an array of silicon detectors and electronics that can be conformed onto a curved surface. That curved surface, much like the human eye, can serve as the focal plane array of the camera, which captures an image.
On a standard digital camera, these electronics have to lie on a flat surface. As a result, the camera’s lens system must reflect an image multiple times before it can reflect on the correct points on the focal plane.
The question Huang and Rogers confronted was how to place those electronics on a curved surface and still have a working camera. It’s a problem with which scientists have struggled over the past two decades. The electronics involved lie on silicon wafers, which can only be compressed 1 percent before they break and fail.
The World Is Not Flat, It Just Seems That Way
The solution was to create an array of photodetectors and circuit elements that are so small — approximately 100 micrometers square — that they are not as affected when the elastomer pops back into its hemispheric shape. The researchers liken the electronics to buildings on the Earth — though flat buildings are built on the curved Earth, the area they take up relative to the Earth’s size is so small that the curvature under them is negligible.
They also designed the array so that the silicon component of each device is sandwiched in the middle of two other layers. This is known as the “natural mechanical plane.” So while the top layer is stretched and the bottom layer is compressed, the middle layer experiences very little stress.
“The novelty is that we are able to conform convention 2-D, planar optoelectronics technologies onto curvilinear surfaces, such as those of a hemisphere. This type of capability can open up new design avenues for advanced camera systems in which not only the lenses but also the geometrical layouts of the detector arrays can be optimized for performance,” Huang explained.
The lenses are made in a two step-process. First comes the fabrication of planar detector arrays in deformable “mesh” layouts, in which rigid, silicon based detectors are electronically interconnected by flexible plastic ribbon cables between 1 and 2 microns thick. Then an elastomeric element is used reshape these meshes from the flat, planar configuration in which they are fabricated into the hemispherical shape for integration into the electronic camera eye.
“The devices that we were able to achieve involve the detector arrays conformally integrated with a hemispherical surface, with the size, geometry and overall layout of the human eye. The imaging characteristics of these devices are better than those possible with planar layouts, when simple, single component optics [are] used,” he continued.
Early images taken using the curved array in an electronic eye-type camera showed large-scale pictures that are much clearer than those obtained with similar, but planar, cameras, when simple imaging optics are used, he said
“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,” Huang pointed out.