LightR: A Fault-Tolerant Wavelength-Routed Optical Networks-on-Chip Topology

Optical networks-on-chip (NoCs) have emerged as a next-generation solution to overcome the limitations of electrical NoCs. In particular, wavelength-routed optical networks-on-chip (WRONoCs) are well known for their high bandwidth and ultra-low signal delay. Despite these advantages, WRONoCs are challenged by reliability concerns, because the main components in WRONoCs, i.e., microring resonators (MRRs), are susceptible to fabrication inaccuracies. When an MRR along a signal path is defective, the signal transmitted on that path will fail to reach its designated destination, which leads to transmission errors and data loss. In this work, we propose a fault-tolerant WRONoC topology, LightR, which provides two independent signal paths for each master-slave pair to tolerate defective MRRs. Moreover, we minimize the MRR usage to enhance the reliability of the WRONoCs. The experimental results show that LightR is able to provide a higher reliability with a modest MRR usage, insertion loss, and crosstalk noise. As the fault rate or the network size grows, the advantages of LightR in terms of the fault tolerance become even more significant. For example, when considering the 3% fault rate of MRRs and a 64-master x 64-slave network, LightR decreases the number of error signals by 85-90% compared to the typical state-of-the-art WRONoC topologies.