Optical Interconnections Between Integrated Circuit Chips

A major limitation to achieving significant speed increases in VLSI lies in the metallic interconnects. They are costly not only from the charge transport standpoint but also from capacitive loading effects. The Defense Advanced Research Projects Agency, in pursuit of fifth generation supercomputing, is investigating alternatives to the VLSI metallic interconnects, especially the use of optical techniques to transport the information between chips or between boards. As the on‐chip performance of VLSI continues to improve via the scale‐down of the logic elements, the problems associated with transferring data off and onto the chip become more severe. The use of optical carriers to transfer the information within the computer is very appealing from several viewpoints. Besides the potential for gigabit propagation rates, the conversion from electronics to optics conveniently provides a decoupling of the various circuits from one another. Significant gains will also be realised in reducing cross‐talk between the metallic routings, and the interconnects need no longer be constrained to the plane of the VLSI chip. In addition, optics can offer an increased programming flexibility for restructuring the interconnect network.