Cameras Without Lenses
It sounds odd to think of cameras without lenses to focus the light, because cameras have continually been created with intent to replicate the eye, and the eye has a lens. Without a lens, how do you focus light? Well you don't, but that's ok, because you don't have to.
The back of the retina is covered with hundreds of thousands of rods and cones, each of which detects light, colour, or luminance. If the density was much greater than it is in the eye, we wouldn't need to focus light to determine the picture, we could just aggregate the input to each and every cone.
That is what a MIT breakthrough has done; creates a material that is essentially millionso f nanoscale cones. They are light detecting fibres, that can be assembled into woven materials. They are advantageous because they overcome many of the limitations of lenses. Lenses are fragile, they are hard to make small enough to fit inside miniature endoscopes, and, in addition, they possess a host of intrinsic aberrations, such as astigmatism, spherical and chromatic aberration, coma, and other intrinsic problems.
The fibre senses light across its cross section, not at the end. This means the entire length of the fabric is detecting light, and attempting to build up a composite picture. It opens up the possibility of fabric strips instead of webcams, and combat fatigues that serve as 360 degree video cameras. Assuming of course, the computing power is on hand to disentangle the images produced.
In a recent issue of the journal Nanoletters, the researchers, led by Associate Professor Yoel Fink of the Department of Materials Science and Engineering (DMSE), reported what it called a "significant" advance: using such a fiber web to take a rudimentary picture of a smiley face.
"This is the first time that anybody has demonstrated that a single plane of fibers, or 'fabric,' can collect images just like a camera but without a lens," said Fink, corresponding author of the Nanoletters paper. "This work constitutes a new approach to vision and imaging."
"We are saying, 'instead of a tiny, sensitive object [for capturing images], let's construct a large, distributed system,'" said Fink. "While the current version of these fabrics can only image nearby objects, it can still can see much farther than most shirts can," he added.
The new fibers, less than a millimetre in diameter, are composed of layers of light-detecting materials nested one within another.
Those layers include two rings of a semiconductor material that are light sensitive, each ring only 100 billionths of a meter across. Four metal electrodes contact each of the rings, extending along the length of the fiber, for a total of eight. Each semiconductor ring with its attached electrodes is in turn encased in rings of a polymer insulator that separate it from its neighbour.
The team starts with a macroscopic cylinder, or preform, of these elements. That preform is placed into a special furnace that melts the components, carefully drawing them into minuscule fibres that retain the original orientation of the various layers. The process can produce many meters of fibre.