Photonic Switching Technologies, Architectures, and Integrated-Systems for Future Disaggregated and Optically Reconfigurable Data Centers

This Tutorial covers technologies, architectures, and system-integration for future data centers with optical reconfigurability. Optical interconnects allow disaggregation of computing resources in the data centers thanks to distance-independent energy-efficient and high-throughput communications of photonics. Photonic switching can provide additional benefits of reconfigurability of the interconnection topologies without requiring electronic-switches that accompany store-and-forward mechanisms. Hence, the primary motivation for considering photonic switching in data centers rises from the need for energy-efficient and scalable intra-data center networks to meet rapid increases in data traffic driven by emerging applications, including machine learning. To accommodate such traffic, today's large-scale data centers employ cascaded stages of many power-hungry electronic packet switches interconnected across the data center network in fixed hierarchical communication topologies. Numerous research papers have predicted significant benefits in scalability, throughput, and power efficiency from deploying photonic switches in data centers. However, photonic switching is not yet widely deployed in commercial warehouse-scale data centers at the time of writing this Tutorial due to significant challenges. They are related to (1) cross-layer issues involving control and management planes together with data integrity during switching, (2) scalability to > 5000 racks (> a quarter-million servers), (3) performance monitoring required for reliable operation, (4) currently existing standards allowing limited power margin (3 dB), and (5) other practical (technology-dependent) issues relating to polarization sensitivity, temperature sensitivity, cost, etc. We will discuss possible solutions for future data centers involving cross-layer methods, new topologies, and innovative photonic switching technologies. Furthermore, the Tutorial broadly surveys state-of- the-art photonic switching technologies, architectures, and experimental results, and further covers the details of arrayed- waveguide-grating-router-based switch fabrics offering hybrid switching methods with distributed control planes towards scalable data center networking.