UC San Diego

Today’s data center networks operate at the cutting edge of fiber optic link and electronic packet switching capabilities. The immense bandwidth requirements of next-generation data centers will stress the limits of electronic switching, providing an opportunity for transparent optical switching to deliver an overall cost-bandwidth advantage. However, current optical switching approaches are not optimal for data center networks because they either do not scale to large port count, reconfigure too slowly, or introduce insertion loss or crosstalk levels incompatible with cost-effective optical transceivers. This dissertation presents the design and demonstration of a novel optical switch architecture more well-suited to data centers, along with the design of overall network architectures that employ this new switch architecture.

The dissertation begins at the physical layer with a scalability assessment of conventional microelectromechanical systems (MEMS) based beam-steering optical switching. MEMS beam-steering cross-connects are the only optical switching technology which has demonstrated the large port count and broadband, polarization-insensitive transmission necessary to approach the scale and link power budgets of modern data center networks. The shortcoming of conventional cross-connects is their slow reconfiguration time, which prevents them from effectively provisioning bandwidth on the timescales necessary for a potentially large fraction of data center traffic. First-principles analysis at the device level indicates that, rather than a straightforward redesign of existing crossbar switches, entirely new switch architectures are necessary to meet the optical switching performance required for data centers.

Motivated by physical layer analysis, a novel selector switch architecture is presented which, through an unconventional approach of relaxing the degree of switch configurability, allows MEMS beam-steering switching elements to scale to microsecond-class response speeds while supporting large port count and low loss switching. The switch is partially configurable in that it selects port mapping patterns from a small hardware library of preconfigured mappings, rather than implementing arbitrary mappings like a crossbar. The physical architecture of the switch uses pupil-division and relay imaging, permitting designs compatible with single-mode or multi-mode fiber optics. The design, fabrication, and experimental characterization is presented for a proof-of-principle prototype using a single MEMS comb-driven micromirror to achieve 150 microsecond switching of 61 single-mode ports between 4 preconfigured port mappings. The scalability of this switch architecture is demonstrated with the detailed optical design of a low-loss 2,048-port selector switch with 20 microsecond switching time.

Because conventional network architectures are typically based on crossbar switches, new overall network architectures are required to utilize the partial configurability of selector switches. The dissertation concludes with an investigation of network architectures based on selector switches, showing, perhaps unexpectedly, that partially configurable networks can deliver aggregate bandwidth approaching that of a fully-provisioned electronically-switched network for common network traffic patterns, but for reduced cost, cabling complexity, and power consumption.

The approach taken in this dissertation of developing switch and network architectures which balance scalability at the physical layer and performance at the network layer will hopefully aid in the design of future optical data center networks.