July 27, 2006 — Digital cameras may have supplanted their analog cousins, but now a new optical imaging method could one day replace digital.
A crisscrossing web of transparent, light-detecting fibers developed by scientists at the Massachusetts Institute of Technology senses the direction, intensity and phase of light in three-dimensional space without any lenses, filters or detector arrays typically used for the task.
The lightweight fibers could be used to make everything from space telescopes that unfurl sail-like imagers, to interactive computer screens that respond to light instead of mouse clicks, to electronic clothing capable of sensing the environment better than the wearer.
"We have shown already that these very simple fiber arrays can extract images without a lens," said Yoel Fink, an associate professor of materials science at MIT.
Fink, with postdoctoral associate Ayman Abouraddy and colleagues, published the results in a recent issue of Nature Materials.
In conventional imaging systems, the lens is a crucial component, as it focuses the light onto the detector surface, whether that is a light-sensitive film or computer chip.
But in Fink's system, a software algorithm does the work of the lens after light hits the photo-detecting fibers.
"It's a completely new way of doing things," said Eli Yablonovitch, professor of electrical engineering at University of California, Los Angeles.
The fibers, 1 millimeter in diameter, are comprised of three elements: a semiconducting core flanked by metal conductors, all encircled in an insulating shell of a polymer.
Weaving the fibers together produces a screen-like product with unique coordinates for each location where two fibers intersect. With this method, scientists can pinpoint where on the grid light is being shined.
Placing one screen in front of another — or forming one screen into a sphere as the team did in laboratory tests — provides even more detail.
As light passes through a coordinate on the facing screen and through another coordinate behind, the scientists determine where the light came from by drawing an imaginary line through the two coordinates.
At the same time, the fiber is collecting information about the light, including its intensity and the frequency of the light waves. A software algorithm calculates how the light would change if it passed through a lens and uses the answer to generate a picture of the light's source.
And whereas conventional imaging systems have a limited field of view, Fink's system is able to sense light coming from all directions.
"The beauty of this is that they are able to make this three-dimensional detection and to do so with an object that is essentially transparent," said Malvin Teisch, professor of physics and electrical and computing engineering at Boston University.
Fink's team is currently working on fibers that can sense a wider range of light wavelengths — in order to produce color images — as well as ones that can read heat and sound.
