Minimal pixels achieve the highest possible resolution visible to the human eye

As the transfer of information in our society becomes more complex, so the demand increases for screens that transmit images and video with precision. Researchers from Chalmers University of Technology, the University of Gothenburg and Uppsala University, Sweden, have developed a screen technology with the smallest pixels ever and with the highest resolution possible for the human eye to perceive.

The pixels reproduce colors using nanoparticles whose dimensions and arrangement control how light is scattered, and whose optical properties can be electrically tuned. This breakthrough, presented in a paper published in Nature, paves the way for the creation of virtual worlds that are visually indistinguishable from reality.

“The technology that we have developed can provide new ways to interact with information and the world around us. It could expand creative possibilities, improve remote collaboration, and even accelerate scientific research,” says Kunli Xiong, Associate Senior Lecturer/Assistant Professor at the Department of Materials Science and Engineering at Uppsala University, who conceived the project and is the lead author of the study.

It is the size and number of pixels that determine the resolution, and thereby how realistic images and films displayed on screens can be. In virtual or augmented reality, where the screen is small and close to the eye, the experience is limited by the fact that today’s pixels cannot be made small enough. On a micro-LED screen, for example, pixels work poorly when they become smaller than 1 micrometer in size.

To overcome this, the researchers present retina E-paper, a new type of electronic paper, or reflective screen. Each pixel is approximately 560 nanometers and the overall screen area is comparable to the size of the human pupil, with a resolution of beyond 25,000 ppi (pixels per inch).

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

The retina E-paper can be placed very close to the eye. To demonstrate the technology’s performance, researchers recreated an image of Gustav Klimt’s famous artwork “The Kiss” on a surface area of approximately 1.4 × 1.9 millimeters. By way of comparison, this means that the image was 1/4000th that of a standard smartphone.

As in previous research led by Dahlin, the screen is passive, meaning that it does not contain its own light source; instead, the colors of the pixels appear when ambient light hits small structures on a surface. The same principle can be found in the magnificent plumage of small birds.

The ultrasmall pixels contain particles of tungsten oxide. By adjusting the size of the particles and how they are positioned in relation to one another, the researchers have succeeded in controlling how the colors in light are diffused and reflected, thereby creating pixels in the colors red, green and blue, which can then be used to generate all colors. By applying a weak voltage, the particles can be “switched off” and they will turn black.

“This is a major step forward in the development of screens that can be shrunk to miniature size while improving quality and reducing energy consumption. The technology needs to be fine-tuned further, but we believe that retina E-paper will play a major role in its field and will eventually have impact on us all,” says Giovanni Volpe, Professor at the Department of Physics at the University of Gothenburg.