Friday, February 08, 2008

Large-Scale Rewritable Holograms

Continued from page 1

By Kevin Bullis

Researchers have tried making rewritable holographic displays in the past, but they faced a number of problems. Materials failed to produce bright images, for example, or the images faded quickly. Peyghambarian's new materials can preserve an image for hours and produce very bright images. The materials can also be easily made in large areas. The prototype holographic film created with the new material is 10 centimeters on a side, but because it was made using well-known polymer processing techniques, it should be relatively easy to scale it up to much larger sizes, says Joseph Perry, a professor of chemistry and biochemistry at Georgia Tech.

The process currently takes a few minutes to write and erase an image--much too long for video. But it might be possible to significantly increase the write and erase speed, says Perry. There are two key limitations right now. One is how fast the electric fields can be established, which is determined by how fast the holes can move. Next, once the fields are in place, it takes some time for the dye molecules to rotate. One way to improve the speeds is to amplify the other property of the dye that changes the behavior of light--the change in polarization. Right now, this is a small effect, but the polarization changes very quickly--fast enough to change the image in real time, Perry says.

For many applications, the new approach will face stiff competition from a growing number of 3-D technologies that can already display video and, like the new approach, do not require that the viewer wear special equipment. That could limit the applications of the new display to those that don't require fast updates, such as maps, says Brian Schowengerdt, a research scientist at the Human Interface Technology Laboratory at the University of Washington. Peyghambarian's approach could also have an advantage for very large displays, since the other technologies are difficult to make that size. These could be used for high-end marketing displays, says Neil Dodgson, the director of studies in computer science at Emmanuel College, part of the University of Cambridge.

"People already spend a lot of money on holograms," Dodgson says. "An updatable one would be a fantastic advertising medium."