A brand new variety of OLED (organic light emitting diode) could replace bulky night vision goggles with lightweight glasses, making them cheaper and more practical for prolonged use, based on University of Michigan researchers.
A memory effect within the OLEDs could also result in computer vision systems that each sense and interpret incoming light signals and pictures.
Current night vision systems depend on image intensifiers that convert incoming near-infrared light into electrons, which then speed up through a vacuum right into a thin disc containing a whole lot of tiny channels. As they go through and collide with the channel partitions, the electrons release 1000’s of additional electrons and go on to strike a phosphor screen, which converts them into visible light. The incoming light is amplified by 10,000 times on this process, allowing the wearer to see at night.
The newly developed OLED device also converts near infrared light into visible light and amplifies it greater than 100 times, but without the burden, high voltage and cumbersome vacuum layer required for traditional image intensifiers. The researchers say much higher amplification is feasible by optimizing the design of the device.
“Probably the most attractive features of this latest approach is that it amplifies light inside a skinny film stack that’s lower than a micron thick. That is much thinner than a strand of hair, which is about 50 microns thick,” said Chris Giebink, U-M professor of electrical and computer engineering and physics and corresponding writer of the study recently published in Nature Photonics.
Since the device operates at much lower voltage than a standard image intensifier, it opens the door to significantly reducing power consumption and thereby extending battery life.
The device works by integrating a photon-absorbing layer, which converts infrared light into electrons, and a five-layer stack of OLEDs, where those electrons are converted into visible light photons. Ideally, five photons are produced for every electron that passes through the OLED stack.
A few of these photons are emitted out to the user’s eye, but others are reabsorbed back within the photon-absorbing layer, producing still more electrons that move through the OLED in a positive feedback cycle. This chain response greatly amplifies the quantity of output light that results for a given amount of input light.
Previous OLEDs were in a position to convert near infrared light to visible light, but there was no gain, meaning one input photon yielded one output photon.
“This marks the primary demonstration of high photon gain in a skinny film device,” said Raju Lampande, U-M postdoctoral research fellow in electrical and computer engineering and lead writer of the study.
The device also exhibits a kind of memory behavior that would have applications in computer vision. Often known as hysteresis, its light output at a given moment is dependent upon the intensity and duration of past input illumination.
“Normally while you illuminate an upconversion OLED, it starts outputting light and while you turn off the illumination, it stops outputting light. This device can get stuck on and remember things over time, which is unusual,” Giebink said.
Although the memory behavior introduces some challenges for night vision applications, it could create a chance for image processing that works more just like the human visual system — where biological neurons pass signals on, or not, based on the timing and strength of incoming signals. The flexibility to recollect past inputs could make these OLEDs a great candidate for the variety of neuron-like connections that enable an input image to be interpreted and classified without having to process the information in a separate computing unit.
The researchers fabricated the device using “off the shelf” materials and methods which can be already widely utilized in OLED manufacturing, which should improve each cost effectiveness and scalability for future applications of the technology.
The work was carried out in collaboration with OLEDWorks, an organization that manufactures OLED lighting products, and RTX, an aerospace and defense contractor. The technology is patent-pending by OLEDWorks and Penn State University, where the study originated before Giebink moved to U-M. This research was funded by DARPA (Award No. HR0011-22-C-0053).
