In a paper in the scientific journal Nature, researchers from the University of Gothenburg, Chalmers University of Technology and Uppsala University (Sweden) present the technology with the smallest pixels yet, the highest resolution display the human eye can perceive. The pixels reproduce colours using nanoparticles whose size and arrangement control the scattering of light and whose optical properties can be electrically adjusted. This breakthrough paves the way for the creation of virtual worlds that are visually indistinguishable from reality.

As the transmission of information in our society becomes increasingly complex, the demand for displays that transmit images and video with high fidelity is growing.

“The technology we have developed can bring new ways of interacting with information and the world around us. It can expand creative possibilities, improve remote collaboration and even accelerate scientific research,” says Kunli Xiong, Assistant Professor at Uppsala University’s Department of Materials Science and Engineering, who initiated the project and is the lead author of the study.

Electronic paper

Resolution, or how realistic images and movies can be on screens, is determined by the size and number of pixels. In virtual or augmented reality, where the display is small and close to the eye, the experience is limited by the fact that we can’t make today’s pixels small enough. For example, on a micro-LED display, pixels perform poorly when they are less than one micrometer in size. However, in the paper “Video-rate tunable colour electronic paper with human resolution” published in Nature, the researchers present Retina E-paper, a new type of electronic paper – a reflective display. Each pixel is approximately 560 nanometres in size and the total area of the display is comparable to the size of a human pupil, with a resolution in excess of 25 000 ppi (pixels per inch).

Illustration of a display in front of the eye and the rays of light hitting the retina.
Illustration of a pupil-sized display, inspired by the human retina, with ultra-high resolution and sub-micrometer pixels.

Millimetre art

“This means that each pixel roughly corresponds to one photoreceptor in the eye, i.e. a nerve cell in the retina that converts light into biological signals. Humans cannot perceive higher resolution,” says Andreas Dahlin, professor in the Department of Chemistry and Chemical Engineering at Chalmers.

Retina E-paper can be placed very close to the eye. To demonstrate the power of the technology, the researchers recreated an image of Gustav Klimt’s famous work “The Kiss” on an area of approximately 1.4 × 1.9 millimetres. For comparison, the image was about 1/4000 the size of a standard smartphone.

Tungsten oxide

As in previous research led by Andreas Dahlin, the display is passive and contains no light source of its own. The colours of the pixels appear when ambient light hits the tiny structures on the surface. The same principle is found in the beautiful plumage of tiny birds. The ultra-small pixels contain tungsten oxide particles. By adjusting the size of the particles and how they arrange themselves, scientists have managed to control how colours scatter and reflect in the light, creating pixels in red, green and blue that can be used to piece together all the colours. When a weak voltage is applied, the particles can be “switched off” and turn black.

“This is a significant step forward in the development of displays that can be shrunk to miniature sizes, while improving quality and reducing power consumption. The technology still needs to be fine-tuned, but we believe that Retina E-paper will play a major role in its field and will eventually affect us all,” says Giovanni Volpe, professor at the Department of Physics at the University of Gothenburg.

Source: University of Gothenburg

Full scientific paper in Nature: video-rate tunable colour electronic paper with human resolution