Parviz Soltan sometimes sounds more like a sorcerer than a physicist. Imagine that you hold in your hand a transparent cube, he says, palm outstretched. This is the television screen of the future, in which you will see three-dimensional images from any direction.
For now, Soltan’s palm is empty, but he has managed to build a much larger forerunner of a magic cube. In his lab at the U.S. Navy’s Command, Control, and Ocean Surveillance Center near San Diego, he proudly displays a three-foot-tall glass cylinder. Underneath, images come to life in the full glory of their three dimensions. Unlike holograms, which can be viewed from only a narrow angle of perspective, Soltan’s volumetric display re-creates a little three-dimensional world in miniature. You can stand on tiptoe and look down at the scene, squat down and peer up at it, or walk around it to see the other side.
Heavy cables link Soltan’s cylinder to the two-foot-square box of lasers, optics, and computers needed to produce the three-dimensional images. Though cumbersome, this prototype is nevertheless almost as functional as the elegant little cube Soltan envisions. The glass cylinder encloses a short, squat plastic double helix--two spirals--18 inches high and 24 inches in diameter. The helix spins ten times each second, fast enough to make it invisible. Mirrors placed at the top of the cylinder reflect pulses of light from a dozen red, green, and blue laser beams down into the helix. The helix creates a visible point of light by re-reflecting a beam. The device constructs images by creating up to 120,000 such points- -Soltan calls them voxels, for volume picture elements--20 times each second.
A key breakthrough was finding a way to direct the laser beams this way and that quickly enough to make sufficient voxels for a decent image. First Soltan experimented with a wide variety of contraptions, including motorized mirrors, which were much too slow. Then he hit upon tellurium dioxide crystals. The key characteristic of this well-known material is that light passing through it tends to slow down as the density of the crystal increases. Soltan could thus bend a laser beam passing through the crystal simply by modifying the pressure on the crystal with ordinary sound waves.
All that was left for Soltan to do was to convert data representing the three-dimensional image into sound waves to control the laser beams. The machine turns the sound on, turns it off, repositions everything, and does it all over again in microseconds. A computer keeps track of when the helix blade passes a zero point and how fast it’s going, explains Robert Belfatto, vice president of NEOS Technologies, the Melbourne, Florida, firm that helped the Navy develop the system. Then it sends the right voxel to the right place at the right time.
The first primitive version of this three-dimensional television will be available by year’s end for the bargain-basement price of $85,000. That may be too much for the average couch potato, but not for industrial design labs, airports, and theme parks hungry for the latest in three- dimensional display technology. Soltan is currently experimenting with air traffic data to monitor flights at San Diego Airport. As many as 85 airplanes appear at any one time within the cylinder as points of light suspended in midair.
When five planes arrive at a busy airport, traffic controllers may see them on a radar screen, one piled on top of another, Soltan points out. Controllers have to determine the altitude of each one to see if any are too close to each other. With our display, they know at a glance. In the future, he hopes to use the TV to convert magnetic resonance snapshots of patients’ tissues into three-dimensional pictures for doctors and to turn engineering blueprints into tangible objects. From sonograms, we could even show an unborn baby in the birth canal, Soltan says.
He still has work to do before he can offer the world a magic cube. For one thing, his display lags behind the best two-dimensional cathode-ray tubes in its ability to resolve fine detail. Eventually, Soltan hopes to switch to a cube-shaped display that Stanford researchers are developing. The solid glass or plastic cube is infused with rare earth phosphors, which emit light when struck simultaneously by two infrared laser beams. That way, we can put a voxel anywhere in the cube, Soltan says. A bona fide magic cube would not be far behind. The breakthroughs have been made, he says. All that remains is to replace good parts with better parts.
