Performance scaling comparison for free-space optical and electrical interconnection approaches.

Projected performance metrics of free-space optical and electrical interconnections are estimated and compared in terms of smart-pixel input-output bandwidth density and practical geometric packaging constraints. The results suggest that three-dimensional optical interconnects based on smart pixels provide the highest volume, latency, and power-consumption benefits for applications in which globally interconnected networks are required to implement links across many integrated-circuit chips. It is further shown that interconnection approaches based on macro-optical elements achieve better scaling than those based on micro-optical elements. The scaling limits of micro-optical-based architectures stem from the need for repeaters to overcome diffraction losses in multichip architectures with high bisection bandwidth. The overall results provide guidance in determining whether and how strongly a free-space optical interconnection approach can be applied to a given multiprocessor problem.