Promise of Holographic Displays

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The Promise of Holographic Displays

By Sandrine Ceurstemont

Commissioned by CACM Staff, June 1, 2023

Unlike today's two-dimensional computer screens, holographic displays could soon present images that appear to be in three dimensions.

The next generation of computer screens could incorporate holographic displays, allowing us to interact with images and videos that appear to be presented in three dimensions.

Instead of interacting with real-time videos of colleagues during videoconferences, they could be represented as holograms. Medical professionals could be presented with three-dimensional (3D) views of organs and scans to help diagnose conditions and plan surgeries. Holographic representations are also of interest for defense applications, to better visualize a battlefield when preparing missions.

"The promise of holography is to project images that you can almost not distinguish from reality," says Theo Marescaux, founder and chief product officer of Swave Photonics, a fabless semiconductor company based in Leuven, Belgium.

Holography can be thought of as photography's 3D counterpart. Whereas a photo captures the varying intensity of light in a scene, a hologram also incorporates the light's phase—a light wave's position in its cycle at a point in time—which allows a 3D image to be recreated. In traditional holography, a light beam from a coherent light source such as a laser, which emits light waves of the same phase, is split in two to illuminate a scene. A hologram can then be produced by recording the interference pattern of the two beams. With computer-generated holography, algorithms can be used to simulate the process in order to create holographic displays.

Virtual reality (VR) is often considered to be a competing technology since it also aims to mimic the real world. VR headsets provide a stereoscopic view and typically track a user's head pose to make them feel immersed in a virtual scene. However, when creating the illusion of depth, virtual objects at certain distances often look blurry, since there can be a mismatch between their perceived location in space and the focusing distance, which is the screen from which they are being projected. The discrepancy can also make users feel nauseous after long-term use. In contrast, "With holography, you don't have that because you're reconstructing the entire image with perfect focus at any point in space," says Marescaux.

Furthermore, virtual reality generates a 3D view for a single user, whereas holographic displays could create virtual objects capable of being viewed by many people simultaneously. "You could have different perspectives represented in a big format display [so that] people can look at things from different angles," says Kaan Aksit, an associate professor at University College London in the U.K., who is researching 3D display technologies.

Challenges

There are challenges to overcome, however, before holographic displays can be made real. One is that generating holograms is computationally expensive, since all the light rays in a 3D scene, passing through every point of every object and in every direction, must be recorded and reconstructed, including all the depth cues perceived by the human eye. Supercomputers have been used to create accurate simulations of the underlying physics, but even so it can take minutes to produce a single holographic image.

To speed up the process, Liang Shi, a Ph.D. student in the Computer Science and Artificial Intelligence Laboratory (CSAIL) of the Massachusetts Institute of Technology (MIT), worked with colleagues to develop a deep learning method called tensor holography that can reduce the amount of computation required.

The researchers first created a dataset containing 4,000 images, with color and depth information for each pixel of each image, and a corresponding 3D hologram for each image. They then trained their deep learning model with the pairs of visuals, after which the system was able to uncover the underlying relationship between an image and its holographic counterpart.  ... '