Visual displays are becoming bigger, brighter and sharper than ever with the development of new display lighting technologies. However, most of the displays we encounter are only two-dimensional and lack any depth information. While improvements in the resolution of 2D displays can help create more realistic images, being able to recreate depth information would be very beneficial for creating truly immersive visual experiences.
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There are several different technologies to recreate 3D images, including multiview, volumetric and holographic displays.1 Many of these are still based on the same concepts that were used in the earliest attempts to create 3D displays which is the use of slight variations in the images projected to the left and right eye to create the perception of depth in the image.
Of the available 3D display technologies, holographic displays arguably have the greatest potential to create highly realistic and detailed images. Another advantage of 3D holographic displays is that they do not require the use of aids such as 3D glasses to see the image in 3D. There are a number of different ways to store the 3D holographic information from which the 3D image will later be reconstructed.
Ways to generate 3D images include the use of micro-electro-mechanical systems (MEMS) where the individual mechanical ‘pistons’ move to either ‘up’ or ‘down’ states to change the diffraction pattern of the light and therefore the appearance of the hologram.2 Each piston represents an individual pixel.
Other approaches include laser-plasma technologies that can be used to generate ‘free floating’ 3D images.
The Data Problem
The main challenge with creating detailed 3D holograms is dealing with the volume of data. This includes both storing the information for the hologram and reading it to reconstruct the image.
For a fairly simple 256-color image rendered at a 60 Hz refresh rate on a 70 cm screen, a 3D hologram demands nearly 1016 bits of data per second.3 This is nearly ten orders of magnitude more data than simple black and white television and becomes very challenging to create particularly 3D holograms that are animated.
The data volume is also problematic for scaling 3D holographic displays. Any increase in screen size or resolution means further increasing the amount of data that must be stored and processed.
Other issues include creating holograms with suitably wide fields of view so that they can truly mimic the normal human viewing range. Trying to achieve similar fields of view as an average person has is an important component in recreating immersive experiences with such displays.
Holobricks
Recently, researchers have proposed the use of so-called ‘holobricks’ to create a modular 3D holographic display system with seamless tiling between modules.4
The holobricks are self-contained coarse integral holographic displays. Each holobrick contains a spatial light modulator, a scanner and some integral optics.
The use of the high bandwidth spatial light modulator with the periscopic coarse integral optics in each of the holobricks means a wide viewing angle 3D hologram can be generated from each module.
As the optics system is designed to impose an upper limit on the size of the projected hologram, the image never exceeds a given area, and in this way, the different holobrick modules can be brought together to create a larger, seamless image.
One of the big challenges for producing 3D holographic displays has been the need to make fringe patterns with sufficient space-bandwidth products to mean they would be viewable at a reasonable number of angles. The space-bandwidth product is a measure of the information in a signal versus the rendering capabilities of the optical system.
Technical Developments
While the work on holobricks is not the first time that spatial light modulators have been utilized in a 3D holographic display, producing spatial light modulators that could result in light with ample space-bandwidth products has been a challenge.
The team did not try and address the issues of the coarse pitch and small area of the spatial light modulator, but instead made use of its wide bandwidth in conjunction with a specially designed optical layout to create angularly tilted 3D holograms with wide fields of view.
The team trialed a number of different optical layouts for the holobricks, but some were capable of achieving a bandwidth of 71.9 bit s-1. This would then be further linearly scalable by adding more holobricks.
Overall, the holobricks showed good performance in a range of visualization tasks, including 2D holographic images, 3D holographic stereograms of physical objects, and 3D holograms of computer-generated objects. The excellent performance, combined with the scalability of the system means that this may become one of the future architectures for 3D displays overcoming one of the greatest challenges for such displays so far – poor scaling with an increased display size of resolution.
References and Further Reading
- Geng, J. (2014). Three-dimensional display technologies. Advanced Optics Photonics, 5(4), 456–535. https://doi.org/10.1364/AOP.5.000456
- Takaki, Y. (2015). Super multi-view and holographic displays using MEMS devices. Displays, 37, 19–24. https://doi.org/10.1016/j.displa.2014.09.002
- Blanche, P. (2021). Holography, and the future of 3D display. Light: Advanced Manufacturing, 2, 28 https://doi.org/10.37188/lam.2021.028
- Li, J., Smithwick, Q., & Chu, D. (2022). Holobricks: modular coarse integral holographic displays. Light: Science & Applications, 11(1). https://doi.org/10.1038/s41377-022-00742-7
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