|[February 20, 2013]
New Imaging Device That Is Flexible, Flat, and Transparent
WASHINGTON --(Business Wire)--
Digital cameras, medical scanners, and other imaging technologies have
advanced considerably during the past decade. Continuing this pace of
innovation, an Austrian research team has developed an entirely new way
of capturing images based on a flat, flexible, transparent, and
potentially disposable polymer sheet. The team describes their new
device and its possible applications in a paper published today in the
Optical Society's (OSA)
open-access journal Optics
The world's first flexible and completely transparent image sensor. The plastic film is coated with fluorescent particles. Credit: Optics Express.
The new imager, which resembles a flexible plastic film, uses
fluorescent particles to capture incoming light and channel a portion of
it to an array of sensors framing the sheet. With no electronics or
internal components, the imager's elegant design makes it ideal for a
new breed of imaging technologies, including user interface devices that
can respond not to a touch, but merely to a simple gesture.
"To our knowledge, we are the first to present an image sensor that is
fully transparent - no integrated microstructures, such as circuits -
and is flexible and scalable at the same time," says Oliver Bimber of
the Johannes Kepler University Linz in Austria, co-author of the Optics
The sensor is based on a polymer film known as a luminescent
concentrator (LC), which is suffused with tiny fluorescent particles
that absorb a very specific wavelength (blue light for example) and then
reemit it at a longer wavelength (green light for example). Some of the
reemitted fluorescent light is scattered out of the imager, but a
portion of it travels throughout the interior of the film to the outer
edges, where arrays of optical sensors (similar to 1-D pinhole cameras)
capture the light. A computer then combines the signals to create a
gray-scale image. "With fluorescence, a portion of the light that is
reemitted actually stays inside the film," says Bimber. "This is the
basic principle of our sensor."
For the luminescent concentrator to work as an imager, Bimber and his
colleagues had to determine precisely where light was falling across the
entire surface of the film. This was the major technical challenge
because the polymer sheet cannot be divided into indivdual pixels like
the CCD camera inside a smartphone. Instead, fluorescent light from all
points across its surface travels to all the edge sensors. Calculating
where each bit of light entered the imager would be like determining
where along a subway line a passenger got on after the train reached its
final destination and all the passengers exited at once.
The solution came from the phenomenon of light attenuation, or dimming,
as it travels through the polymer. The longer it travels, the dimmer it
becomes. So by measuring the relative brightness of light reaching the
sensor array, it was possible to calculate where the light entered the
film. This same principle has already been employed in an input device
that tracks the location of a single laser point on a screen.
The researchers were able to scale up this basic principle by measuring
how much light arrives from every direction at each position on the
image sensor at the film's edge. They could then reconstruct the image
by using a technique similar to X-ray computed tomography, more commonly
known as a CT scan.
"In CT technology, it's impossible to reconstruct an image from a single
measurement of X-ray attenuation along one scanning direction alone,"
says Bimber. "With a multiple of these measurements taken at different
positions and directions, however, this becomes possible. Our system
works in the same way, but where CT uses X-rays, our technique uses
Currently, the resolution from this image sensor is low (32x32 pixels
with the first prototypes). The main reason for this is the limited
signal-to-noise ratio of the low-cost photodiodes being used. The
researchers are planning better prototypes that cool the photodiodes to
achieve a higher signal-to-noise ratio.
By applying advanced sampling techniques, the researchers can already
enhance the resolution by reconstructing multiple images at different
positions on the film. These positions differ by less than a single
pixel (as determined by the final image, not the polymer itself). By
having multiple of these slightly different images reconstructed, it's
possible to create a higher resolution image. "This does not require
better photodiodes," notes Bimber, "and does not make the sensor
significantly slower. The more images we combine, the higher the final
resolution is, up to a certain limit."
The main application the researchers envision for this new technology is
in touch-free, transparent user interfaces that could seamlessly overlay
a television or other display technology. This would give computer
operators or video-game players full gesture control without the need
for cameras or other external motion-tracking devices. The polymer sheet
could also be wrapped around objects to provide them with sensor
capabilities. Since the material is transparent, it's also possible to
use multiple layers that each fluoresce at different wavelengths to
capture color images.
The researchers also are considering attaching their new sensor in front
of a regular, high-resolution CCD sensor. This would allow recording of
two images at the same time at two different exposures. "Combining both
would give us a high-resolution image with less overexposed or
underexposed regions if scenes with a high dynamic range or contrast are
captured," Bimber speculates. He also notes that the polymer sheet
portion of the device is relatively inexpensive and therefore
disposable. "I think there are many applications for this sensor that we
are not yet aware of," he concludes.
a transparent, flexible, scalable and disposable image sensor using
thin-film luminescent concentrators," A. Koppelhuber and O. Bimber, Optics
Express, Vol. 21, Issue 4, pp. 4796-4810 (2013)
EDITOR'S NOTE: Images are available to members of the media upon
request. Contact Angela Stark, firstname.lastname@example.org.
About Optics Express
Optics Express reports on new developments in all fields of
optical science and technology every two weeks. The journal provides
rapid publication of original, peer-reviewed papers. It is published by
the Optical Society and edited by Andrew M. Weiner of Purdue University (News - Alert). Optics
Express is an open-access journal and is available at no cost to
readers online at www.OpticsInfoBase.org/OE.
Uniting more than 180,000 professionals from 175 countries, the Optical
Society (OSA) brings together the global optics community through its
programs and initiatives. Since 1916 OSA has worked to advance the
common interests of the field, providing educational resources to the
scientists, engineers and business leaders who work in the field by
promoting the science of light and the advanced technologies made
possible by optics and photonics. OSA publications, events, technical
groups and programs foster optics knowledge and scientific collaboration
among all those with an interest in optics and photonics. For more
information, visit www.osa.org.
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