A new method of capturing images based on a flat, flexible, transparent, and potentially disposable polymer sheet has been developed by a team of researchers at Johannes Kepler University Linz in Austria.
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 simple design makes it ideal for a new breed of imaging technologies, including user interface devices that can respond to gestures (touch not required).
“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 team leader Oliver Bimber.
The sensor is based on a polymer film known as a luminescent concentrator (LC). It 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 individual pixels like the CCD camera inside a smartphone. Instead, fluorescent light from all points across its surface travels to all the edge sensors.
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.
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.