Proceedings Article | 7 August 2023
KEYWORDS: Holograms, Waveguides, Holographic displays, Holographic optical elements, Digital holography, Eye tracking, Liquid crystal on silicon, Computer generated holography, Holographic materials, Volume Bragg gratings, Planar waveguides
In this work, we present a proof of concept Holographic Near Eye Display (HNED) that can, in principle, be very thin (few mm’s), have high resolution, enlarged eye box, provide wide Field of View (FOV), correct for the user’s prescription, and display 3D content, and thus avoid the Vergence-Accommodation Conflict (VAC). This optical architecture combines a Holographic Optical Element (HOE) waveguide, a Liquid Crystal over Silicon (LCoS) acting as a digital dynamic hologram, eye tracking, and Display Exit Pupil steering and switching. The waveguide expands the beam and acts as a front illuminator for the LCoS. So a small in-coupling element to the waveguide can illuminate the large area of the digital hologram. Several static multiplexed holograms were recorded within the in-coupling and out-coupling HOEs of the waveguide. The static in-coupling holograms did not contain any power, while the static out-coupling holograms had a lens function with around 35 mm focal distance. In-coupling and out-coupling static holograms were matched in pairs and met the Bragg condition at the same horizontal angle. The digital hologram, i.e., the LCoS, was illuminated with the converging illumination emerging from the static out-coupling hologram. The light was focused at a different position in the eye box for each static multiplexed hologram. Thus, by knowing the position of the user’s eye, the angle beam incident on the in-coupling element was adjusted, and the correct out-coupling element directed the light into the user’s eye pupil. Steering in the vertical direction was achieved by utilizing the “Bragg Degeneracy”1 of the static holograms.
