On the routing and scalability of MZI-based optical Beneš interconnects

Abstract Silicon Photonic interconnects are a promising technology for scaling computing systems into the exa-scale domain. However, there exist significant challenges in terms of optical losses and complexity. In this work, we evaluate the applicability of a thermally/electrically tuned Benes network based on Mach–Zehnder Interferometers for on-chip and inter-chip interconnects as regards its scalability. We examine how insertion loss, laser power and switching energy consumption scale with the number of endpoints. In addition, we propose a set of hardware-inspired routing strategies that leverage the inherent asymmetry present in the switching components. We evaluate a range of network sizes, from 16 up to 256 endpoints, using 8 realistic and synthetic workloads and found very promising results. Our routing strategies offer a reduction in path-dependent insertion loss of up to 35% in the best case, as well as a laser power reduction of 31% for 32 endpoints. In addition, bit-switching energy is reduced by between 8% and 15% using the most efficient routing strategy, depending on the communication workload. We also show that workload execution time can be reduced with the best strategies by 5%–25% in some workloads, while the worst-case increases are at most 3%. Using our routing strategies, we show that under the examined technology parameters, a 32-endpoint interconnect can be considered for the NoC domain in terms of insertion loss and laser power, even when using conservative parameters for the modulator.