EAGER: Tackling the Variations and Instability of Nanophotonic Interconnection Network via Architecture Techniques

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In current designs of computer chips, electrical wires are used for communication between the different components of the chip. As technology scales down into the nanometer domain, the signal delay and power consumption caused by electrical wires start to dominate the overall delay and power consumption on the chip, mainly because wires do not scale as well as other logic components. A promising alternative to using electrical wires is to use optical waveguides for communication. Using nanophotonics for on-chip communication may lead to faster signal propagation, increased bandwidth density and reduced power consumption. However, many fundamental challenges face the integration of optical devices into commercial chips. This project addresses some of these challenges and its success will have a significant impact on the semiconductor industry.The two major challenges addressed in this project are process variations and thermal sensitivity of optical devices. The former refers to the drifts in resonance wavelengths of optical devices due to fabrication errors during the manufacturing process. The latter refers to similar drifts that result during operation due to temperature fluctuations within the chip. Both drifts are inevitable with current technology and cause the optical network to lose significant bandwidth. Instead of relying on device level innovations, the proposed research takes an architectural approach to endure and tolerate drifts in wavelength resonance. Specifically, it investigates different techniques to maximize the effective bandwidth at run-time in the presence of defects and changes in operating temperatures. These techniques treat bandwidth as a resource that is allocated, on-demand, to different nodes in a way that masks the resonance shifts of optical devices. Since the aggregated available on-chip bandwidth is usually larger than the instantaneous demand for bandwidth, the effect of the imperfect hardware is mitigated by appropriately assigning wavelengths to nodes, thus offering a reliable and near perfect optical communication layer to the other components of the system.