We report the first demonstration of a complete 16 x 16 strictly nonblocking guided-wave optical switching system. The system, based on a three-stage Extended Generalized Shuffle Network, includes 448 directional coupler switch elements in 23 packaged modules. The modules are mounted in a single equipment cabinet and are controlled with a PC-based switching algorithm. We report results of extensive measurements on device and system performance. The devices and system exhibited low uniform voltages, low loss, low crosstalk, and broad bandwidth. This lithium niobate based system operated continuously and without maintenance for a period of 20 months.
Several different shuffle-equivalent interconnection topologies that can be used within the optical link stages of photonic-switching networks are studied. These schemes include the two shuffle, the two banyan, and the segmented two shuffle, which can be used to interconnect two-input, two-output switching nodes. The schemes also include the four shuffle and the four banyan, which can be used to interconnect four-input, four-output switching nodes. (Note: The segmented two shuffle and the four banyan are novel interconnection topologies that were developed to satisfy some of the constraints of free-space digital optics). It is shown that each of these interconnection topologies can be implemented by the use of relatively simple imaging optics that contain space-invariant computer-generated binaryphase gratings. The effects of node type and interconnection topology on the laser power requirements and the optical component complexity within the resulting systems are also studied. The general class of networks nown as extended generalized shuffle networks is used as a baseline for the analysis. It is shown that (2, 1, 1) nodes and (2, 2, 2) nodes connected by two-banyan interconnections can produce power-efficient and cost-effective systems. The results should help identify the architectural trade-offs that exist when a node type and an interconnection topology are selected for implementation within a switching system based on free-space digital optics.
We describe a new optoelectronic switching system demonstration that implements part of the distribution fabric for a large asynchronous transfer mode (ATM) switch. The system uses a single optoelectronic VLSI modulator-based switching chip with more than 4000 optical input-outputs. The optical system images the input fibers from a two-dimensional fiber bundle onto this chip. A new optomechanical design allows the system to be mounted in a standard electronic equipment frame. A large section of the switch was operated as a 208-Mbits/s time-multiplexed space switch, which can serve as part of an ATM switch by use of an appropriate out-of-band controller. A larger section with 896 input light beams and 256 output beams was operated at 160 Mbits/s as a slowly reconfigurable space switch.
Since Clos gave the first construction of a strictly nonblocking multistage interconnection network, only a few other constructions have been proposed in almost a half-century. In this paper, we introduce a constructive class of networks which utilizes crossbars of virtually any size and for which the sizes can vary from stage to stage. The interconnection between stages is a generalized shuffle pattern. We derive sufficient conditions for strictly nonblocking operation and suggest the potential for wide application of these networks by providing several special case results.
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