Display Evolution
The evolution of our various display technologies is shown in the diagram below, which spans a decade of research and development. It starts with simple segmented displays, rather like a calculator or a clock, but the resolution of these is limited. We then progress on to planar displays with increased resolution at different depths in space. The next stage is to make a denser planar display that approximates a volumetric display which stack these planes in slices, like a loaf of bread. Finally, we have light field displays which divide up the volume radially, like a cake.
Light Field Display
We built a 5.5” (~14 cm) flat panel light field display prototype, shown below. It is based on a 4K (3840x216 pixels) phone LCD panel with a pixel density of 806 ppi (pixel/inch). This panel was combined with an optical lenslet array (lenticular) with a field of view of 49 degrees. This display has 110 views with an angular pitch of 0.5 degrees into this FoV. This is a horizontal parallax 3D display i.e. the 3D effect is perceived along the horizontal axis only. Most LF displays on the market take this approach.
Holoxica 5.5” dense Light Field Display
This display produces dense and detailed light field, which poses many challenges for image generation. Our Holoviewer software was intially designed to render a large number of views for digital hologram technology, whose light field density is orders of magnitude higher. Holoviewer was then adapted for real-time 3D graphics for this demanding high (angular) resolution display, which is performed with a Light Field Processing Unit (LFGPU) based on high-end graphics cards.
Holoxica has partnered with other companies to offer commercial light field displays that work with our software suite.
Volumetric Display
Our third generation holographic display leveraged the work we have done with the previous generation of planar displays. The aim was to create a volumetric space in mid-air with independently addressable voxels in (x,y,z). If these voxels are sufficiently numerous and dense, then this will approximate a volumetric display.
The volumetric display is designed to visualise images from medical scanners (CT, MRI, Ultrasound). This project, HoloMedical3D, was supported by the European Commission Horizon 2020 SME Instrument Phase2 grant. The technology is based on a large-area diffractive optical element, high speed projector and a multi-wavelength light source. We aimed to build a basic prototype for validation in several medical scenarios including education, diagnostics, monitoring and surgical planning. The project led to a paper, patent and software for visualising medical imagery. This software was later rolled into our Holoviewer framework aimed at next gen Light Field displays. We published in Optic Letters in 2019: “Volumetric 3D display in real space using a diffractive lens, fast projector, and polychromatic light source.”
Planar Interactive HUD-style display
Holoxica's second generation technology is an Interactive Holographic 3D Display. The design is inspired by Head-Up Displays (HUDs), based on free-space optics with images floating in mid-air that can change in real-time. A paper on this display was presented at the SPIE (International Photonics Society) Photonics West Conference in February 2013, and was published in the conference proceedings.
The first interactive holographic display prototype comprises a large area Holographic Optical Element (HOE) lens, a digital controller, a motion sensor and a projection subsystem (a laser projector). The HOE is about the size of an A4 page (20x30cm) and the images are formed in real space about 20cm from the hologram plane. The image are about the size of a hand (up to 7x7cm). The images can be refreshed at video rates and arbitrary images can be displayed. However, the images are formed in three distinct planes, corresponding to the colours of the lasers in the laser projector i.e. red, green and blue.
The display includes a Kinect motion sensor to enable interactivity with a number of apps that we have written for it. The viewer can ‘touch’ icons in space and do things like draw in mid-air. We have ten apps including mid-air drawing, pong-style game, counter, keypad, viewing image sequences and more.
The second prototype is a more compact mini-HUD unit, based on a 100 mm DOE (Diffractive Optical Element) and an RGB laser pico-projector, similar to the previous architecture. The DOE was manufactured using a novel Diamond Turning technology from the University of Strathclyde.
Segmented Holographic Display
Holoxica's first generation holographic display was first demonstrated in 2010, working in collaboration with Heriot Watt University and Edinburgh University. The display is based on holograms at its heart where a fixed number of different holograms are sampled and interwoven into the holographic screen. Any of the pre-configured images can be selected in any order to make "flip motion" 3D animation giving the impression of motion. The resulting 3D image is suspended in mid-air and can change in real time.
The display embeds up to nine images but this can be scaled up. Colour can be realised by combining red, green and blue light sources.
Applications for the segmented display included clocks, virtual icons or simple signage. This technology is patented and is available for licensing to partners.