After the computation is complete, the output is fed to the light modulator. The introduction of a novel modulator, says Bove, is a primary reason he and his team have been able to shrink the holographic setup. The modulator is an inexpensive device adapted from use in telecommunications; Daniel Smalley, a graduate student in Bove’s lab, modified its components, optimizing them to convert electrical signals into holographic patterns. Previous holographic systems used up to 18 separate modulators that were made of expensive materials and took up a lot of space. The new device, says Bove, is about half the size of a postage stamp. It’s fast and can accommodate a large amount of data, allowing for high-resolution holograms.
When light from a laser or set of lasers enters the modulator, it’s converted into a series of diffraction patterns that are shaped and focused by a number of lenses and mirrors before they reach the screen. One of the advantages of the new modulator, explains Bove, is that it allows the researchers to avoid using a bulky rotating mirror that previous setups required to keep a holographic scene from drifting horizontally. That mirror was “the bane of the two early generations of [holographic] video display,” he says. Now that it’s been eliminated, Quinn Smithwick, a postdoc in the lab, has figured out how to shorten and fold the system’s optical path so that the necessary components fit into a space about half a meter long.
Currently, Mark III uses a gas laser housed in a foot-long tube. But in its final version, it will use a semiconductor laser as small as a postage stamp. Bove says the system will project a monochromatic video scene, about the size of a snapshot photo, that will have the resolution of a standard television image.
Aware that this sort of display wouldn’t cut it in consumer applications, Bove and his team have laid out plans for the next generation of the system, Mark IV. Mark IV will use a set of powerful red, blue, and green semiconductor lasers to shine full-color videos onto a screen the size of a computer monitor. A prototype could be ready within the next couple of years.
The market, of course, will dictate how quickly, if ever, holographic video makes its way into living rooms or doctor’s offices. If all goes well, however, it could give doctors a better window into the body, let scientists visualize data more accurately, and help gamers immerse themselves more deeply in virtual worlds.