Dynamic Reconfiguration of Silicon Photonic Circuit Switched Interconnection Networks

Silicon photonic interconnection networks can provide significant advantages in bandwidth densities and data communication energy efficiencies over electronic-interconnected systems. However, due to the circuit switched nature of photonics, the latencies associated with circuit setup and reconfiguration must be managed to avoid added delays in application execution time. This work characterizes circuit setup latencies and explores architectural solutions and methodologies for amortizing the setup latencies. We first collect data on the initialization delay of an end-to-end silicon photonic link using the latest generation of Field Programmable Gate Array (FPGA) hardware to control a Mach-Zehnder interferometer (MZI)based 2x2 switch and a microring-based demultiplexing filter. We demonstrate nano-second scale broadband switching for wavelength division multiplexing (WDM), and a scalable FPGAbased method for wavelength locking and thermal stabilization of the microring demultiplexer. The burst-mode receiver synchronization time of the FPGA is also measured for a 20 Gbps datapath. Using the collected data we then estimate the overall delay to set up an optical circuit, and investigate the effects of a circuit management technique to amortize this delay. The technique is adapted from cache optimization and relies on a metric called circuit reuse distance (CRD). Reuse distance profiles are generated based on a group of representative HPC applications with different communications patterns, and the potential to amortize circuit setup delay over multiple circuit requests is shown. Simulations show that a Markov transition matrix based reuse distance prediction method has significantly higher accuracy than traditional maximum likelihood prediction. Additionally, we show that two replacement policies using Markov chain prediction effectively increase the hit rate compared to the least recently used policy. Keywords— circuit switched; reuse distance; silicon photonics; initialization; replacement; cache; RDMA; FPGA