Speed and energy analysis of digital interconnections: comparison of on-chip, off-chip, and free-space technologies

We model and compare on-chip (up to wafer scale) and off-chip (multichip module) high-speed electrical interconnections with free-space optical interconnections in terms of speed performance and energy requirements for digital transmission in large-scale systems. For all technologies the interconnections are first modeled and optimized for minimum delay as functions of the interconnection length for both one-to-one and fan-out connections. Then energy requirements are derived as functions of the interconnection length. Free-space optical interconnections that use multiple-quantum-well modulators or vertical-cavity surface-emitting lasers as transmitters are shown to offer a speed-energy product advantage as high as 30 over that of the electrical interconnection technologies. (C) 1998 Optical Society of America.