Transparent heads-up displays are used in airplanes to provide important flight data to pilots and in cars to provide driving directions directly on the windshield. Researchers have developed a new approach for heads-up displays that are holograph-based, making the screen much easier to see with a large eye box.
The current heads-up displays have a small eye box. This means that most of the information being shown disappears at least partly if the driver or pilot shifts their gaze.
"A heads-up display using our new technology installed in a car would allow a driver to see the displayed information even if he or she moved around or was shorter or taller than average," said research team leader Pierre-Alexandre Blanche of the University of Arizona.
The researchers have developed a functional prototype heads-up display that takes advantage of holographic optical elements to develop an eye box that is larger than the current eye box.
"Increasing the size of either the eye box or the displayed image in a traditional heads-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," said first author Colton Bigler, a doctoral student in Blanche's laboratory. "Instead of relying on conventional optics, we use holography to create a thin optical element that can be ultimately applied to a windshield directly."
The laser light interactions that can be used to create the proactive holograms on credit cards can be used to create optical elements like lenses and filters in materials that are light sensitive. The holographic elements the researchers used are smaller than the traditional optical components and are easily mass produced.
In the new display, the holographic optical elements redirect light from a small image to a piece of glass. The image stays there until another holographic optical element extracts the light. This extraction hologram makes the image viewable to the larger eye box.
"We are working with Honeywell to develop these displays for aircraft, but they could just as easily be used in cars," Blanche said. "Our approach requires no expensive equipment and no new materials need to be developed. Furthermore, the display can be completely integrated into a standard car windshield."
The researchers’ lab version of the display has an eye box that is seven times larger than the eye box of current displays. The next stop for the researchers was to make a working prototype that can display flight information on a piece of glass as part of the transparent enclosure that covers cockpits. With the prototype, the researchers doubled the eye box of the original image, as well as proving that the image doesn’t display until the user looks past the edge of the hologram. They showed that the image shown appears in the far field. Basically, pilots or drivers don’t need to change focus to see the information on the display.
"It's possible to create a much larger eye box by increasing the size of the injection and extraction holographic elements, the only limitation is the size of the glass displaying the image," Blanche continued. "Our work is a good example of how holography can be used to solve many types of optical problems for various applications. A similar approach might also be useful for augmented reality headsets, which also merge computer-generated images with views of the outside world but with a display that is close to the eye."
The lab version of this display only shows one color, but the researchers say they can develop full-color heads-up displays. Currently, they are trying to develop this approach for a larger image that is extracted by the holographic elements to increase the size of the display.
The paper on this research was published in Applied Optics.