Mission Apollo: Landing Optical Circuit Switching at Datacenter Scale

TL;DR

Apollo is the first large-scale deployment of optical circuit switches in datacenters, addressing infrastructure challenges with innovative design to meet bandwidth, scale, and cost requirements.

Contribution

This paper introduces Apollo, a novel large-scale optical circuit switching system for datacenters, including its design, implementation, and deployment details.

Findings

Successful deployment of optical circuit switches at datacenter scale

Achieved high bandwidth and scalability with cost-effective design

Demonstrated effective bidirectional links using circulators

Abstract

In this paper, we describe Apollo, to the best of our knowledge, the world's first large-scale production deployment of optical circuit switches (OCSes) for datacenter networking. We will first describe the infrastructure challenges and use cases that motivated optical switching inside datacenters. We then delve into the requirements of OCSes for datacenter applications: balancing cost, port count, switching time, and optical performance, which drive design choices and implementation details of our internally developed 3D MEMS-based OCS. To enable the Apollo optical switching layer, we employ circulators to realize bidirectional links through the OCS, effectively doubling the OCS radix. The OCS and circulator design choices were critical for meeting network bandwidth, scale, and cost targets. We review the critical co-design of WDM transceiver technology for these OCS plus circulator-based bidirectional links and their corresponding physical impairments, delivered over four generations/speeds of optical interconnect. Finally, we conclude with thoughts on future directions in hardware development and associated applications.