The Connection Machine computer has 65536 processors interconnected through a hypercube network. In commercial systems, current costs make short-distance optical fibers attractive only when connector density or wire density are critical. The prototype utilized a 400-Mb/s optical interconnect consisting of two fibers to provide the interprocessor communication between two 8 K processor subcubes. A 1100-Mb/s link will be completed by the end of 1989. In this case, optical interconnects provided over two orders of magnitude improvement in connection density. The architecture, design, and physical characteristics of a prototype optical interconnect for the Connection Machine are described. The future use of optical interconnections in computer systems is explored.>