Crystal Clear Holographic Video
Many research teams are working to innovate holographic video, but Benton’s Spatial Imaging Group at MIT has long been at the field’s forefront. Here, various students and staff have been looking at the problem from every angle, so to speak, for 13 years. In recent years the main sponsors of the research have been the U. S. Navy, which believes its wartime decision-makers would benefit from looking at a 3-D representation of a battle landscape, and Honda, which hopes its car designers will be able to produce 3-D images of proposed new models rapidly. “When we first approached Honda, we were amazed to find out they had already been thinking of holography,” says Benton.The MIT effort has from the beginning focused on true holographic video, which not only holds out the promise of the highest-quality 3-D video images, but also provides the most daunting technical challenges. At its core are the basic steps of creating a standard hologram: A laser beam is split in two. One half is directed at an object-let’s say, an apple. The presence of the apple distorts the pattern of light waves in the beam, modulating it. That beam is then made to intersect with its other half in light-sensitive material. When the two beams overlap, their differing patterns of light waves interfere with each other, etching a diffraction pattern of microscopic lines onto the light-sensitive material. The diffraction pattern works like a complicated lens. When a laser beam illuminates it, the microscopic lines reflect the light in a way that produces a
3-D image of the apple.
Instead of light and mirrors, Benton and his team use specially developed computer algorithms. The algorithms calculate the kinds of microscopic lines necessary for a certain hologram, convert them into sound waves, and then send the waves into a stack of tellurium-oxide crystals that have the unique property of distorting temporarily when sound waves pass through them. That distortion forms the microscopic lines of the diffraction pattern that make up a hologram. A laser beam passing through that pattern conveys the image from the crystals to a view screen (see “MIT’s Mark II Holographic Video,” below).
MIT’s Mark II Holographic Video Display produces surprisingly pleasing and lifelike 3-D images. In one demo, a red prototype sports car designed by Honda instantly appears to hover brightly in miniature a half-meter or so in front of the observer, all of the car’s graceful lines perfectly discernible from different angles. Perhaps it’s partly because of the novelty of the experience, but the mild flicker and shimmering image bars hardly distract attention from the intense realism of the effect.
Benton’s group is continually making refinements in three core areas: hardware and software for the display, realism and image quality, and interactivity. Wendy Plesniak, a Media Lab researcher and consultant who as a student helped develop computing algorithms for the holographic video device, added a feature that could ultimately lead to an industrial designer’s dream machine: a haptic, or force feedback, interface that makes it possible to “sculpt” the projected image with a real-life, handheld tool. As the user pokes, prods, and carves with a stylus, the holographic image changes as if it were clay on a potter’s wheel, and the user senses resistance as if she were really working the clay.