What does a spatial light modulator do, and what will it be able to do in the future? Quite a lot, according to the world-renowned Battelle Memorial Institute of Columbus, Ohio, which conducted a feasibility study of Ronald Kirk's SLM. In the first report issued after that study was completed, one research scientist wrote: "The development of a device capable of electronically detecting, storing, transmitting, and reconstructing holographic information would represent a major breakthrough of tremendous importance to applications involving coherent optical processing, pattern recognition, nondestructive testing, and many other optical applications. The Holotronics concept is potentially capable of providing that breakthrough. . . ."
An SLM is a small, electro-optical device that converts electronic signals into the equivalent of an instant transparency of the object under observation, thus allowing the generation of a holographic image. By impressing a two-dimensional array of information onto a light beam -- usually instantaneously, and usually temporarily -- it accesses this information to a light processor. This, in turn, makes possible certain manipulations, such as pattern recognition and optical computing. The faster the process, the closer "real time" is approached. Some SLMs, like Litton Industries Inc.'s, are magnetically switched devices. Others rely on thermal heating units or integrated circuitry. The Holotronics Corp.'s Optical Tunnel Array uses an electronic switching system and may be the most advanced unit yet developed. At any rate, the National Aeronautics and Space Administration is very high on the long-run potential of the Holotronics technology.
Relatively little is known, however, about the technology's short-term potential and benefits. One reason is that much research in the field has been conducted under military auspices, where security is paramount. Using a sophisticated SLM with high-speed imaging capabilities, for instance, an "intelligent" missile guidance system could be developed whereby optical scanners could pick out the physical characteristics of any desired target (e.g., a specific type of tank, ship, or airplane) and deliver the warhead to it. Or, an optical processor with a built-in SLM could be used against a high-powered jammer that was disrupting radio communications, detecting and removing the jamming signal in a matter of microseconds.
In the commercial area, the SLM will probably have its major effect in the fields of optical processing and robotics. According to William E. Ross, who invented Light-Mod, an SLM, in 1977 for Litton's Data Systems Division, "Three-dimensional robotic vision will make artificial intelligence real. With optical processing in real time, robots will be able to make decisions in a manner similar to the way in which human beings do. Humans receive a lot of information simultaneously, which leads to the parallel thought processes that produce decisions. With real-time optical vision, robotics will truly come of age."
Ron Kirk concurs. "Up until now, industrial robots have been manually programmed. They could be programmed to pick up a bolt and screw it into socket A, but if the bolt came up sideways on the conveyor belt, the robot would try to insert it sideways. Now they're more sophisticated: They can tell if it's out of position, and reorient it. But total optical processing is a whole different ball game. By [using an SLM to create a high-speed sequence of filter transparencies], you could have a robot that would take a box of machine parts, open it up, lay out all the parts, and assemble a motor."
And the potential in holography is not just industrial, either. "I imagine," says Kirk, "the time when a heart patient will lie down on a table with a holographic recording system beneath him -- one employing as the source of energy not visible light, but ultrasound, X rays, or microwaves. The surgeons will then be able to project in real time a hologram of the working heart. By fine-tuning the ultrasound, they could even look past the muscle tissue and examine specific internal areas for obstructions to blood flow, embolisms, anything. No exploratory surgery, no angiograms. As long as you have a high enough resolution quality to the image, just about anything is possible."