Ultrahigh-definition digital 3D holographic display
Holographic displays generate realistic images exhibited in a 3D environment which can be perceived by the naked eye. In conventional holographic display systems, the perceivable viewing angle and the volume size of 3D images were small due to a limited number of pixels in display devices. Here, a novel 3D holographic display system was proposed by exploiting the technique of multiple light scattering. The randomly scattered lights were modulated to help project the resulting 3D images; these representations feature an enhanced viewing angle and image size over conventional holographic displays. This new type of holographic display may open the avenue for the practical holographic displays.
In recent years, 3D display has been drawing much interest and fascination from the general public due to the advancement of VR/AR display technology. Head-mount 3D displays for example, exploit a binocular disparity to the viewer’s pair of eyes. The projected images are two different 2D images rather than accurate 3D images; this approach therefore simplifies the display devices. Due to the incomplete representation of 3D image information, however, viewers have reported feeling visually fatigued after long-term use. An ultimate 3D display should work without special glasses and should project realistic images that involves comfortable viewing conditions. Holography display is a promising method to realize realistic 3D imaging because the hologram replicates exactly the real world scenes; the viewer therefore cannot distinguish between the hologram and the actual object/scene.
Although the development of holographic display has been studied for several decades, current digital holographic display technology is still premature for use in daily life. The main limitation of current 3D displays is the limited viewing angle and image size. In order to present a realistic 3D image, the pixel density in the display devices should be enhanced; a factor of 10,000 times improvement in density is demanded over what 2D LCD monitors currently provide.
In order to solve the practical issues of digital holographic displays, researchers at KAIST led by Professor YongKeun Park have exploited complex light scattering to project enhanced 3D images. When light is scattered at the surface of optical diffusers, volume speckle fields having a large scattering angle and large volume are generated due to the multiple light scattering. At the initial state, only diffusive lights are observed without any meaningful 3D images formed. Interestingly, multiple light scattering behaves in a linear and deterministic manner. If the light scattering process is precisely measured, then 3D images can be generated by controlling the pattern of incident light.
By characterizing the complex light scattering process in optical diffusers, the researchers have generated 3D images with the viewing angle of 35° within a 2 x 2 x 2 cm3 volume using a deformable mirror. This enhanced image size and viewing angle, generated with a single deformable mirror and diffusers, are effectively equal to the viewing condition that can be obtained from an array of 2,600 deformable mirrors. However, the decrease in the image contrast due to the presence of speckle background needs to be overcome and must be addressed in future studies. The researchers expect that the proposed idea can pave the way for a popularization of 3D holographic displays.
This study was published in Nature Photonics (March, 2017).
 Yu, H., Lee, K., Park J., Park, Y. “Ultrahigh-definition dynamic 3D holographic display by active control of volume speckle fields.” Nature Photonics 11.3 (2017): 186-192
* Lab information : http://bmol.kaist.ac.kr (Lab webpage)