  Recent advances in integrated photonics enable the implementation of
reconfigurable, high-bandwidth, and low energy-per-bit interconnects in
next-generation data centers. We propose and evaluate an Optically Connected
Memory (OCM) architecture that disaggregates the main memory from the
computation nodes in data centers. OCM is based on micro-ring resonators
(MRRs), and it does not require any modification to the DRAM memory modules. We
calculate energy consumption from real photonic devices and integrate them into
a system simulator to evaluate performance. Our results show that (1) OCM is
capable of interconnecting four DDR4 memory channels to a computing node using
two fibers with 1.07 pJ energy-per-bit consumption and (2) OCM performs up to
5.5x faster than a disaggregated memory with 40G PCIe NIC connectors to
computing nodes.
