Juggling the speed of light.

Researchers have now demonstrated what they describe as the first general-purpose optical computer. This maze of lasers, switches, and optical fibers occupies a space about the size of a desk, stores programs, processes data, and calculates using light instead of electricity Information inside the computer circulates continually in the form of light pulses - except during the brief periods when light pulses are converted into electrical pulses to activate optical switches.

"Previous work in optical computing had not incorporated the stored program, although there have been optical processors:' says Harry E Jordan of the Optoelectronic Computing Systems Center at the University of Colorado at Boulder, who along with Vincent P. Heuring heads the development team there. The researchers can program their optical computer to multiply numbers and perform other simple operations.

"Our computer has [roughly] the power of a mid-60s minicomputer," Jordan notes. "It's got a very small memory. so only simple programs can fit into the machine - but they are stored and interpreted optically, It demonstrates the principle that all of the components of a general-purpose machine can be done in optics."

The optical computer's most striking feature is that no data are ever stored- even temporarily-in particular locations in a memory chip, as they would be in an electronic computer. Instead, information circulates as light pulses through optical fiber loops. "For the first time, we have a computer in which the program and data are always on the fly in the form of light, eliminating the need for static storage," Jordan says. He compares this mode of operation to a square dance, in which everyone is moving and partners must wait until they're next to each other to do the required figure.

With its instructions and data encoded as hundreds of thousands of light pulses, the computer has nearly 5 kilometers of optical fiber serving as its main memory It also has 66 optical switches. During processing, infrared laser beams route light pulses from memory through the switches.