A team of engineers from Taiwan seem to have overcome one of the most persistent challenges of 3D display technology, which could enable them to produce a cinematic 3D display with superior quality compared to most current systems. Their proposed design combines a prism-patterned projection screen with advanced projection technology to achieve both high optical efficiency and low image crosstalk – two properties that have been considered mutually exclusive until now.

The researchers, led by Wallen Mphepö from National Chiao Tung University in Hsinchu, Taiwan, and Chalmers University of Technology in Göteborg, Sweden, have published their proposed 3D display design in a recent issue of IEEE’s Journal of Display Technology.

The new display uses a prism-patterned 3D screen, a technology which has previously been explored to varying degrees of success. In this system, the prism’s angular surfaces reflect light at two different angles, which are received by a viewer’s left and right eyes, creating a sense of depth through parallax. The prism screen can display 3D images to multiple viewers, as long as they are located within a specific distance range from the screen. The system is also autostereoscopic, meaning viewers do not need glasses to see the 3D effects.

The key to prism-based 3D displays is that the prism screen must effectively separate the left and right image pixels. To achieve this pixel separation, the researchers worked on defining the prism angles as well as the curvature of the entire screen, which is necessary in order to keep the rays within the viewing zone. To derive the curvature’s coordinates, the researchers used an iterative process, with each new point on the curved surface computed based on the previous points’ locations.

The initial results of their simulations showed a large amount of crosstalk between left and right viewing zones, meaning that the right eye could see some residue of the image intended for the left eye, and vice versa. In order to minimize the crosstalk, the researchers reconfigured the prism angles to sharpen the reflected rays’ separation. In addition, they slightly increased the inter-ocular separation (the distance between a viewer’s eyes) from 65 to 70 mm, and moved the viewing location to 1.15 m, 50 mm closer to the screen. These measures reduced the amount of overlap between left and right pixels, virtually eliminating the crosstalk.

However, as the engineers note, it’s not the 0% crosstalk that makes the 3D display innovative, but rather the fact that the display also operates at 90% optical efficiency. As Mphepö explained, previous technologies have always assumed that image crosstalk is inversely proportional to optical efficiency.

“In our design you simultaneously get both the desirable high optical efficiency and desirable low or zero crosstalk,” Mphepö told PhysOrg.com. “This bucks the trend and changes the way standard prevailing autostereoscopic 3D display design assumptions that have been in effect up to this point are to be viewed. In short, they no longer apply.”

For instance, as Mphepö explained, a typical autostereoscopic 3D display might use a parallax barrier – a layer of opaque material with slits that is placed in front of the screen, allowing each eye to see a different set of pixels. If the slits are wide, more light can pass through, which increases the optical efficiency. However, wide slits allow more image crosstalk, since each eye sees more light that is intended only for the other eye. On the other hand, making the slits narrower can reduce image crosstalk, but also blocks most of the light, reducing optical efficiency. Thus there is an inherent tradeoff between optical efficiency and crosstalk in such a design.

To overcome this problem, the new system replaces the parallax barrier with fine-tuned prisms that, as Mphepö explained, reflect light to create a “sweet spot” with high optical efficiency and virtually no crosstalk.

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