SPOC-a stored program optical computer

The Digital Optical Computing (DOC) group at the University of Colorado at Boulder have built the world´s first stored program optical computer (SPOC). Several features that distinguish this computer from traditional electronic computers are: the use of optical fibers and pulses of light instead of wires and electronic signals; the use of space and time to store information instead of flip-flops; synchronization based on the predictable propagation time of signals; and return to zero signal encoding. One goal was to show that optics could be used to build a general purpose stored program computer. Another goal was to demonstrate that predictable signal propagation time could replace flip flops for synchronization. The SPOC is a functionally complete computer. The constant speed of light was used to synchronize the signals in the SPOC. We adjusted the length of the input fibers to the logic gates so the signals would arrive at the same time. This synchronization technique is called time-of-flight design. The group developed a design tool, called XHatch, to help design time-of-flight circuits. We used XHatch to determine the lengths of the optical fibers for the SPOC based on its circuit design. The fibers act as registers by storing the signals in space and time until they are fed into a logic element