Jennifer L. Morey
Since its introduction, holography has been stifled by its lengthy and complicated production process and limitations in image quality -- putting it beyond the reach of commercial success. Two companies are hoping to overcome those barriers by developing novel holographic printers that could serve a wealth of industries from graphic design to security.
Using technology developed at the Massachusetts Institute of Techno-logy's Media Lab in Cambridge, Mass., researchers from Zebra Imaging Inc. and Sony have created devices that output holographic stereograms. These 3-D images comprise hundreds of long "strip" holograms that are recorded side by side onto a piece of holographic film. Unlike their predecessors, stereograms can be created directly from photographs or computer graphics.
Traditional holograms require splitting a laser beam in two. One beam reflects off the object and is then recombined with the other half and exposed to a photographic film. This process creates an interference pattern on the film that gives the viewer the impression of a 3-D image when viewed in suitable lighting. However, it also requires a long exposure time and a high-power laser, making it impractical for widespread commercial use.
The MIT researchers hypothesized that they could use a lower-power laser if it were combined with a cylindrical lens to focus the light onto the hologram. Such a configuration created a distorted image, so the scientists predistorted the image electronically to overcome this problem.
Experimental stage
Neither Zebra Imaging nor Sony has a commercial prototype of a holographic printer yet. Sony's monochromatic printer reportedly can produce a hologram up to 8 3 6 cm in about three minutes. The company improved on the MIT work by making its device resistant to vibration and adding a print head system that accurately registers each strip. It plans to test the system soon.
Zebra Imaging has attempted to go one step further by adding color. Color images can be cost-prohibitive because they use three lasers of different wavelengths. Furthermore, they require special film: The company uses a photosensitive polymer film made by DuPont Holographic Materials of Wilmington, Del., that is available for experimental use only. Zebra CEO Alex Ferdman said the company will have a color printer prototype ready by late 1999 that produces a 5 3 7-in. image in under 10 minutes.
The company also can create an image in-house that appears 3-D in both the horizontal and vertical axes -- what is known as a full-parallax image. However, the number of images needed for this type of hologram can create a time problem. Ferdman said the company recently produced a full-color, full-parallax 6 3 18-ft hologram that required 24 hours to produces a single 2 3 2-ft tile. He said the company plans to triple this output speed.
Ferdman said the holographic printers will be marketed primarily to design and marketing firms, but future applications could include CAD/CAM design and portraiture.
