You may be about to see the world in a whole new way. MIT researchers, reporting in this month’s issue of Nature Materials,
have demonstrated that nearly transparent webs made up of novel
semiconducting fibers could replace lenses and sensors in cameras, and,
among other things, lead to uniforms or automobile exteriors that give
people a continuous view of their surroundings.
The
fibers are made of a semiconducting glass core, lined along its full
length by wires that act as positive and negative electrodes, and
surrounded by a transparent polymer (see link to images below). When
light hits the photosensitive core, an electrical current in the fiber
changes, registering the hit.
Advertisement
[Click here for images of this light-sensing fiber.]
This story is only available to subscribers.
Don’t settle for half the story.
Get paywall-free access to technology news for the here and now.
A mesh of these fibers can then be used to identify the location of the light on a surface. In the Nature Materials
paper, the researchers, led by materials scientist Yoel Fink and
physicist John Joannopoulos, demonstrate that the fibers, in addition
to locating a point of light, can be used to determine the direction
from which a light beam comes and can also sense light from a scene to
form an image. “Here’s a structure that’s close to being invisible –
but can see,” says one of the team members, Ayman Abouraddy, a research
scientist at MIT.
For
direction sensing, the researchers formed a grid of fibers into a
sphere. A light beam from a flashlight first hits one side of the
sphere and the grid registers the location. The light then passes
through the sphere and out the other side, where it is detected again.
Then an integrated circuit compares the entrance and exit points to
calculate the path of the light.
Using
a similar technique, the researchers were also able to record a scene,
not just points of light. Light from a scene passes through first one,
then another of two flat, parallel fiber grids, which register the
intensity of light from the scene. However, because there’s no
lens, which in a camera focuses light from a given plane onto a
light detector, the grids receive a blurry image. To compensate for the
lack of a lens, the researchers wrote algorithms that compare slight
differences between the images recorded by the two fiber grids. These
differences allow them to trace the light back to its source – and
mathematically reconstruct an in-focus image. Because this “focusing”
happens after the data has been recorded, it’s also possible to refocus
on various objects in a scene after a picture has been taken.
A
simple manufacturing process makes the fibers inexpensive, and thus it
could be practical to cover large areas with them – even the outside
of buildings. The fibers begin as a “preform,” a long cylinder about as
thick as a spray-paint can that has the same structure (core,
electrode, and polymer) as the finished product, only with a much
larger diameter. The preform is then heated and pulled into
kilometers-long fibers as thin as a tenth of a millimeter. In
developing this method, the researchers had to find materials that
could be drawn into thin fibers at the same temperature without coming
apart. The metal electrodes actually melt during the process, but stay
in place, contained by the polymer and glass.
The
fiber grids are ready now for early single-point light detection
applications, such as being woven into soldier’s uniforms to detect
laser sightings by snipers (see “Material Alert”).
They can also be tuned to detect heat, helping medics locate wounds.
“There’s no more research that needs to go in for this to go into
clothes,” Abouraddy says. “A lot of things you see in papers, there’s a
distance between what you see in the paper and the application. With
these fibers, there’s no distance, this is how they would look.”
Another relatively early application could be incorporating the fibers
into computer screens, allowing speakers giving presentations or
video-game players to control their computers with a laser pointer.
But
Abouraddy says work still needs to be done to make the scene-imaging
capabilities practical. For example, the resolution of the images is
limited by the need to space the fibers within the grid far enough
apart that the first grid does not distort the image received by the
second. The grids themselves also need to be separated, which could
make the current system difficult to incorporate into some
applications, such as on the skin of a car, where keeping the grids at
a distance wouldn’t be practical. But the researchers say work is
currently being done that could overcome these limitations.