Researchers demonstrated a functional prototype head-up display (HUD) that uses optical holographic elements to achieve an eye box substantially larger than what is available without the holographic component. Current head-up displays have a small eye box, which can cause the displayed information to partially or wholly disappear from view if users shift their gaze. The HUD uses holographic elements to redirect light from a small image into a piece of glass, where it is confined until it reaches another holographic element that extracts the light. The extraction hologram presents a viewable image with a larger eye box size than the original. The new head-up display uses holographic optical elements to inject an image into the glass, or waveguide (left). The light enters the glass and bounces back and forth between its front and back edges until it reaches another holographic optical element that extracts a small portion of light that leaves the glass with each bounce (right). The extraction holographic creates a viewable image, with each bounce proportionally increasing the eye box size for the image. Courtesy of Pierre-Alexandre Blanche, University of Arizona. After performing optical simulations, the University of Arizona research team created a laboratory version of their HUD that produced an eye box seven times larger than the original image. The team then built a working prototype that displayed flight information on a piece of glass. The eye box of the original image almost doubled when the prototype with holographic technology was used, and the image did not disappear until the user tried to view beyond the edge of the hologram. In the prototype, the holographic image is presented in the far field, so users do not need to change their focus to view the display. Researcher Colton Bigler said that instead of using conventional optics to increase the size of the eye box, the team used holography to create a thin optical component that ultimately could go directly on a windshield. “Increasing the size of either the eye box or the displayed image in a traditional head-up display requires increasing the size of the projection optics, relay lenses and all the associated optics, which takes up too much space in the dashboard,” he said. Holographic elements are not only smaller than traditional optical components but can be mass-produced because they are easily fabricated. Although the researchers demonstrated their approach using just one color, they say that the technique could be expanded to create full-color HUDs. They plan to make the image that is extracted by the holographic element much larger, thus increasing the field of view. “It’s possible to create a much larger eye box by increasing the size of the injection and extraction holographic elements,” said researcher Pierre-Alexandre Blanche. “The only limitation is the size of the glass displaying the image.” Colton Bigler (right) and Pierre-Alexandre Blanche used holography to improve head-up displays that overlay images onto the windshields of cars and airplanes. Shown here is the laboratory version of their system. Courtesy of Pierre-Alexandre Blanche, University of Arizona. Blanche said that the team is working with Honeywell to develop displays for aircraft. According to the team, the displays could also be used for cars. “Our approach requires no expensive equipment and no new materials need to be developed,” said Blanche. “Furthermore, the display can be completely integrated into a standard car windshield.” The researchers regard their work as an example of how holography can be used to solve many different types of optical problems for various applications. “A similar approach might also be useful for augmented reality headsets," Blanche said, “which also merge computer-generated images with views of the outside world, but with a display that is close to the eye.” The research was published in Applied Optics, a publication of OSA, The Optical Society (doi: 10.1364/AO.57.002007). The researchers built a prototype and showed that it could display flight information on a piece of glass representing a windshield. The image in the background is displayed on a television located 10 meters behind the head-up display system. The beginning of the video shows that the presented image appears in the far field, meaning that observers don’t need to change their focus to see the displayed information. The larger eye box of the display is evident when the camera view moves but the displayed information remains visible until the view moves far off to the side. Courtesy of Pierre-Alexandre Blanche, University of Arizona.