3-D DISPLAYS: Low-cost autostereoscopic screen creates 3-D views

Researchers from Richmond Holographic Studios (RHS, London, England) have demonstrated a practical, full-color, three-dimensional (3-D) computer display. The monitor consists of a hologram attached to a single liquid-crystal-display (LCD) panel, which is illuminated from behind. The hologram reroutes the light transmitted through the LCD into left and right viewing zones and so supplies a 3-D image without the observer having to wear special glasses.

The system, shown at this year's Photonics West (San Jose, CA), has two major advantages over other autostereoscopic systems. First, by simply changing the illumination, the 3-D effect can be supplied to more than one viewer at a time. When combined with a head-tracker, the viewing zones could be made to follow the viewer. Second, unlike lenticular displays, the system never offers the user a pseudoscopic or reverse-depth image. For applications that are not just for entertainment and for which depth is important, this could be crucial. David Trayner and Edwina Orr of RHS have addressed all the basic issues of size, cost, flexibility, and backward compatibility that will determine the technology`s success.

Volumetric displays, which usually involve either light sources or screens moving within a volume, tend to be expensive and bulky and need to be run with special software (and sometimes hardware). Split-screen displays are also bulky and require, effectively, two separate monitors. Lenticular displays appear inexpensive, but they are difficult to implement in color without going to very-high-resolution LCDs, which increases the cost.

System configuration

As currently configured, the RHS system uses alternate horizontal rows of pixels to encode left- and right-eye images.1 Registered against these lines of pixels are the component strips of a holographic optical element that recompile the image onto left and right viewing zones 60 cm from the screen (see figure). Because these zones are determined holographically, the positioning is very accurate. The left and right images abut without a gap or overlap, making a seamless joint; other systems tend to have dark regions between successive images resulting in a "picket fence" effect. The holographic determination of the viewing zones means changing the illumination direction changes the image position, which makes viewer tracking, multiple viewers, and clean two-dimensional viewing possible.

Though the system is currently sufficient to demonstrate the basic principle, much can be done to improve each display component. By switching to an edge-lit holographic format, for instance, the 3-D display could conceivably be small enough to be used in a laptop computer. Choosing the right holographic material will be important, too. The silver halide plates used in the demonstrators are easy to expose, but have low diffraction efficiency and high scatter. Both embossed plastic and photopolymer would have better performance as well as being easier to manufacture. Finally, electronics issues, such as head-tracking and illumination control, have to be resolved. RHS is now actively seeking industrial partners to develop the technology.

REFERENCE

1. D. Trayner and E. Orr, "Autostereoscopic display using holographic optical elements," Proc. SPIE 2653 (March 1996).