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  • Spatial Light Modulator Displays Another Dimension

Photonics Spectra
Oct 1999
Daniel C. McCarthy

Contrary to assertions made in popular culture, outer space is merely the penultimate frontier. The final frontier is virtual space, where three-dimensional real-time images, such as those produced inside volumetric displays, offer applications as widely varied as air traffic control, medical imaging and high-tech video gaming. Future applications are defined only by the limits of human imagination and the available technology. Act Research Corp. is testing those limits with a comparatively low-cost volumetric display that relies on a 256 x 256-pixel spatial light modulator from Displaytech Inc.

Virtual space: the final frontier. A volumetric display from Act Research enables observers to view three-dimensional images without the use of special eyeglasses or helmets. The display uses a high-frame-rate spatial light modulator from Displaytech Inc. Courtesy of Act Research Corp.

Act Research's device produces its computer-generated images in a dome-shaped glass display. Viewing the images requires no special glasses or helmet. Separate viewers can walk around the display, and all see the image simultaneously from multiple viewpoints.

Since the 1960s, the development of volumetric displays has taken various routes, including the use of lasers as a light source. Act Research followed a different approach, modulating light from a metal halide lamp to flash successive picture frames on a rotating two-dimensional screen. Because of the after-image effect of the human eye, the sets of spatially distributed picture frames appear as three-dimensional volumetric images.

"If you use a microchip and a projector, the cost of the system can be very low," explained Che-Chih Tsao, president of Act Research. "Cost is really the major advantage, especially when projection of color images is considered. Of course, size and weight advantages of lamps over lasers are also valid."

Tsao was attracted to Displaytech's spatial light modulator for its high frame rate. The ferroelectric liquid- crystal-based modulator projects optical data onto the display's rotating screen at 2500 frames per second. "We can use any kind of two-dimensional projection panel as long as the frame rate is high enough," Tsao said. "Displaytech is the only choice because they have a high frame rate to create three dimensions."

Act Research's current model is a demonstrational prototype that can image medical data in three dimensions. Tsao explored other liquid crystal modulators but found that their frame rates were too slow. Microarrays, based on active pixel technology, offered an alternative, but, like the lasers, these increased the expense of the system.

"We hope to provide a prototype product for research and development and evaluation markets in about one year," Tsao said. "Our long-term target is to visualize three-dimensional medical data used to guide cancer treatment. We're also interested in computer-aided design and gaming applications."

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