This is Part II of a two-part paper that explores the fundamental limitations on energy consumption in optical communications. Part I covers energy consumption in optical transport. Part II explores the lower bound on energy consumption in optical switches and networks, analyzes the energy performance of a range of switching devices, and presents quantitative models of the lower bounds on energy consumption in these devices. These models are incorporated into a simple model of a global switched network and the lower bound on total network energy consumption is estimated. We compare the results of this bottom-up calculation of the lower bound on network energy with a previous top-down analysis of overall network energy consumption based on real-world data for state-of-the art equipment and “business-as-usual” forward projections. The present analysis confirms a previous finding in that in a global scale network, the energy consumption of the switching infrastructure is larger than the energy consumption of the transport infrastructure. We find that the theoretical lower bounds on transport energy identified in Part I and the switching energy in this paper are more than three orders of magnitude lower than predicted by a “business-as-usual” analysis. In this paper, we explore how the gap between the theoretical lower bounds on energy consumption and current trends in network energy efficiency can be closed. We argue that future research needs to focus on improving the energy efficiency of switching and on devising methods to reduce the quantity of switching infrastructure in the network. Further key strategies for reducing network energy consumption include developing of low-energy transport technologies, reducing the energy overheads associated with peripheral functions that are not central to the transport and switching of data, and reducing the energy consumption of the access network.

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Green Optical Communications—Part II: Energy Limitations in Networks

This paper reviews the work performed under the European ESPRIT project DO/spl I.bar/ALL (Digital OpticAL Logic modules) spanning from advanced devices (semiconductor optical amplifiers) to all-optical modules (laser sources and gates) and from optical signal processing subsystems (packet clock recovery, optical write/store memory, and linear feedback shift register) to their integration in the application level for the demonstration of nontrivial logic functionality (all-optical bit-error-rate tester and a 2/spl times/2 exchange-bypass switch). The successful accomplishment of the project's goals has opened the road for the implementation of more complex ultra-high-speed all-optical signal processing circuits that are key elements for the realization of all-optical packet switching networks.

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All-optical signal Processing and applications within the esprit project DO/spl I.bar/ALL

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.

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

Packet-switching characteristics are optimized across an integrated 4 /spl times/ 4 optical crosspoint switch matrix consisting of active vertical-coupler-based switch cells. Optical gain difference between the shortest and the longest paths less than 3 dB is demonstrated. Bit error rate (BER) and power penalty measurements during packet routing have also been carried out over the entire 4 /spl times/ 4 matrix. At a 10-Gb/s packet data rate, a less than 1-dB power penalty is observed across the switch matrix, and the possibility for error-free packet routing is demonstrated with no BER floor observed.

/pdf/active-vertical-coupler-based-optical-crosspoint-switch-1g91wuyl7q.pdf

Active vertical-coupler-based optical crosspoint switch matrix for optical packet-switching applications

Novel designs for integrated-optic M/spl times/N/spl times/M crossconnect switches are presented and analyzed. Arrays of electroabsorptive microring resonators on a semiconductor chip would provide dense wavelength-division-multiplexed switching in a compact, planar, low-voltage, high-speed geometry. Analysis indicates that the crossconnect is scaleable to 8/spl times/8/spl times/8 with more than 48-dB signal-to-crosstalk ratio.

Proposed N-wavelength M-fiber WDM crossconnect switch using active microring resonators

This paper reviews the various optical space switch structures on III-V semiconductor material. Their characteristics are discussed in the context of optical transport and switching network applications exploiting wavelength division multiplexing.

M. Bachmann

Papers

Semiconductor optical space switches