MIT scientists, including one of Indian-origin, have developed a new
imaging device that consists of a loose bundle of optical fibres, with
no need for lenses or a protective housing.
Bundles of the fibres
could be fed through pipes and immersed in fluids, to image oil fields,
aquifers, or plumbing, without risking damage to watertight housings.
Tight bundles of the fibres could yield endoscopes with narrower diameters, since they would require no additional electronics.
The
fibres are connected to an array of photosensors at one end; the other
ends can be left to wave free, so they could pass individually through
micrometre-scale gaps in a porous membrane, to image whatever is on the
other side.
The positions of the fibres' free ends do not need to correspond to the positions of the photodetectors in the array.
By
measuring the differing times at which short bursts of light reach the
photodetectors - a technique known as "time of flight" - the device can
determine the fibres' relative locations.
In a commercial version
of the device, the calibrating bursts of light would be delivered by the
fibres themselves, but in experiments with their prototype system, the
researchers used external lasers.
"Time of flight, which is a
technique that is broadly used in our group, has never been used to do
such things," said first author Barmak Heshmat, from Massachusetts
Institute of Technology (MIT), who led the new work.
"Previous
works have used time of flight to extract depth information. But in this
work, I was proposing to use time of flight to enable a new interface
for imaging," Heshmat said.
The researchers, including Ramesh
Raskar, used a bundle of 1,100 fibres that were waving free at one end
and positioned opposite a screen on which symbols were projected.
The
other end of the bundle was attached to a beam splitter, which was in
turn connected to both an ordinary camera and a high-speed camera that
can distinguish optical pulses' times of arrival.
Perpendicular to
the tips of the fibres at the bundle's loose end, and to each other,
were two ultrafast lasers. The lasers fired short bursts of light, and
the high-speed camera recorded their time of arrival along each fibber.
Since
the bursts of light came from two different directions, software could
use the differences in arrival time to produce a 2D map of the positions
of the fibres' tips.
It then used that information to unscramble the jumbled image captured by the conventional camera.
The study was published in the journal Nature Scientific Reports.