Large Port Count High-Speed Optical Switch Fabric for Use Within Datacenters [Invited]

This paper reviews advances in the technology of integrated semiconductor optical amplifier based photonic switch fabrics, with particular emphasis on their suitability for high performance network switches for use within a datacenter. The key requirements for large port count optical switch fabrics are addressed noting the need for switches with substantial port counts. The design options for a 16 × 16 port photonic switch fabric architecture are discussed and the choice of a Clos–tree design is described. The control strategy, based on arbitration and scheduling, for an integrated switch fabric is explained. The detailed design and fabrication of the switch is followed by experimental characterization, showing net optical gain and operation at 10 Gb/s with bit error rates lower than 10−9. Finally improvements to the switch are suggested, which should result in 100 Gb/s per port operation at energy efficiencies of 3 pJ/bit.

I. Introduction

The ever increasing requirement for processing, storage and communications capacity within datacenters is putting an ever growing load on the electrical switches and routers used within such centers [1]. in a typical datacenter or warehouse scale computer system each 7’ rack of 40 1U servers is connected via a GbE switch, which uplinks via a 10 GbE link to a cluster switch of much higher capacity [2], as seen in Fig. 1. Energy consumption increases with increasing data rate in these switches, increasing the energy density. As a result the thermal loading issues of current switches and routers are becoming significantly more troublesome as both aggregate data rates and capacities continue to increase. Fig. 1.

(Color online) This figure shows racks of servers, each connected to a switch in the rack. Each of these rack switches is connected via a higher bandwidth connection to a high performance cluster switch, which in turn is connected to a high performance IP router and to the external Internet.