Prospects and challenges of optical switching technologies for intra data center networks

This paper explores how optical switching technologies can innovate future intra data center networks. The effectiveness of applying large-port-count optical switches is clarified by comparing the available scales and performances of electrical and optical switching networks. The two core technologies needed to make it happen are presented: large-port-count optical switches that have pay-as-you-grow scalability and a simple and fast switch control procedure. Different from the present multi-tier electrical switch network, single-tier large-port-count optical switches and their parallel configurations are shown to greatly simplify the network. Their combination offers low blocking rates and low latency even though the connection set-up is performed in a completely distributed and asynchronous manner where network wide synchronization and routing control are unneeded. The design and performance verification of our control network are detailed, and experiments on a control network emulation based on field programmable gate arrays are presented. The connection set-up latency of around 20 µs is verified within a floor (200 m) using our recently developed silicon photonic switch and tunable filter devices. The devices rely on the thermo-optic effect, but if we apply the electro-optic effect and adopt a simplified connection set-up procedure, the set-up latency is reduced to around 7 µs. The direction discussed here will pave the way for achieving bandwidth abundant and energy efficient data center networks in the future.