Increasing the Size of Displays with Stackable ‘Holobricks’

Researchers have developed a new method to display holographic images using ‘holobricks’ that can be stacked together to generate large-scale holograms.

The researchers, from the University of Cambridge and Disney Research, have developed a holobrick proof-of-concept, which can tile holograms together to form a large seamless 3D image.

This is the first time this technology has been demonstrated and opens the door for scalable holographic 3D displays. The results are reported in a paper titled ‘Holobricks: modular coarse integral holographic displays’ in the journal Light: Science & Applications ¹.

The quest for large, animated 3D displays has always been hampered by the need to create a large amount of data flow. To generate a simultaneous large-size and wide-viewing-angle holographic display, a spatial light modulator (SLM) must present a holographic fringe pattern of sufficient space-bandwidth product (SBWP) – the product of fringe pitch and modulation area.

Such a fringe pattern can generate a holographic image with a large optical spread – known as the ‘etendue’, which is the product of field-of-view (FOV) angle and image area.

Unfortunately, the information contained in a holographic image with a very large optical invariant etendue is significantly higher than the modulation capacity of present SLMs with their coarse pixel pitches and small display areas, which deliver a low SBWP.

While, for a 2D full HD display, the information data rate is about three gigabits per second (Gb/s), a 3D display of the same resolution would require a rate of three terabits per second (Tb/s), which is currently not available.

‘Delivering an adequate 3D experience using the current technology is a huge challenge,’ said Prof Daping Chu from Cambridge’s Department of Engineering, who led the research. ‘Over the past ten years, we’ve been working with our industrial partners to develop holographic displays which allow the simultaneous realisation of large size and large fieldof-view, which needs to be matched with a hologram with a large optical information content.’

As previously mentioned, the information content of current holograms is much greater than the display capabilities of current SLMs, due to their limited SBWP.

For 2D displays, it’s standard practice to tile small size displays together to form one large display. The approach being explored by Prof Chu and his team is similar, but for 3D displays, which has not been reported before.

‘Joining pieces of 3D images together is not trivial, because the final image must be seen as seamless from all angles and all depths,’ said Chu, who is also Director of the Centre for Advanced Photonics and Electronics (CAPE). ‘Directly tiling 3D images in real space is just not possible.’ 

To address this challenge, the researchers developed the holobrick unit, based on coarse integrated holographic displays for angularly tiled 3D images, a concept developed at CAPE with Disney Research about seven years ago.

Each of the holobricks uses a high- information bandwidth spatial light modulator for information delivery in conjunction with coarse integrated optics, to form the angularly tiled 3D holograms with large viewing areas and fields of view.

Careful optical design makes sure the holographic fringe pattern fills the entire face of the holobrick, so that multiple holobricks can be seamlessly stacked to form a scalable spatially tiled holographic image 3D display, capable of both wide field-of- view angle and large size.

The proof-of-concept developed by the researchers is made of two seamlessly tiled holobricks. Each full-colour brick is 1024×768 pixels, with a 40° FOV and 24 frames per second, to display tiled holograms for full 3D images.

‘There are still many challenges ahead to make ultra-large 3D displays with wide viewing angles, such as a holographic 3D wall,’ said Chu. ‘We hope that this work can provide a promising way to tackle this issue based on the currently limited display capability of spatial light modulators.’ 

1 - www.nature.com/articles/s41377-022-00742-7.