OLED unlocks compact, lightweight night vision

This new OLED technology may also advance computer vision systems by enabling them to both detect and interpret incoming light and images, thanks to a unique memory effect discovered in the devices.

Traditional night vision systems rely on image intensifiers that convert near-infrared light into electrons, which are then accelerated through a vacuum into a disc with hundreds of channels. As the electrons pass through these channels and hit the walls, thousands of additional electrons are released, ultimately striking a phosphor screen that converts the energy into visible light. This process amplifies incoming light by 10,000 times, making it possible for the user to see in low-light conditions.

In contrast, the newly developed OLED system also converts near-infrared light into visible light but amplifies it over 100 times without the need for heavy equipment, high voltage, or the cumbersome vacuum layer associated with current image intensifiers. The researchers believe they can achieve much higher amplification by refining the device’s design.

“One of the most attractive features of this new approach is that it amplifies light within a thin film stack that is less than a micron thick. That’s much thinner than a strand of hair, which is about 50 microns thick,” said Chris Giebink, a professor of electrical and computer engineering and physics at the University of Michigan, and corresponding author of the study, published in Nature Photonics.

This lower voltage operation could also significantly reduce power consumption, leading to longer battery life for night vision devices.

The OLED system functions by integrating a photon-absorbing layer, which converts infrared light into electrons, with a five-layer stack of OLEDs that convert those electrons into visible light photons. Ideally, the device produces five photons for every electron that passes through the OLED stack. While some of these photons reach the user’s eyes, others are reabsorbed by the photon-absorbing layer, producing additional electrons in a positive feedback loop that amplifies the light.

Previous OLED designs could convert near-infrared light into visible light, but only with a one-to-one photon exchange, resulting in no amplification.

“This marks the first demonstration of high photon gain in a thin film device,” said Raju Lampande, a postdoctoral research fellow in electrical and computer engineering at the University of Michigan and lead author of the study.

In addition to its potential for night vision, the OLED device exhibits memory behaviour that could prove useful in computer vision applications. This behaviour, known as hysteresis, means that the light output at any given time depends on the intensity and duration of past light exposure.

“Normally, when you illuminate an upconversion OLED, it starts outputting light and stops when the illumination is turned off. This device can get stuck on and remember things over time, which is unusual,” Giebink explained.

While this memory feature may pose some challenges for night vision applications, it could enable the device to mimic the human visual system. Biological neurons process signals based on the timing and intensity of inputs, and this OLED technology could enable a similar function, where input images are interpreted and classified without requiring a separate computing unit.

The team manufactured the device using commercially available materials and existing OLED production techniques, which could make it more cost-effective and scalable for future applications.