Asynchronous transfer mode distribution network by use of an optoelectronic VLSI switching chip.

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.

Shuffle-equivalent interconnection topologies based on computer-generated binary-phase gratings.

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.

Five-stage free-space optical switching network with field-effect transistor self-electro-optic-effect-device smart-pixel arrays.

The design, construction, and operational testing of a five-stage, fully interconnected 32 × 16 switching fabric by the use of smart-pixel (2, 1, 1) switching nodes are described. The arrays of switching nodes use monolithically integrated GaAs field-effect transistors, multiple-quantum-well p-i-n detectors, and self-electro-optic-device modulators. Each switching node incorporates 25 field-effect transistors and 17 p-i-n diodes to realize two differential optical receivers, the 2 × 1 node switching logic, a single-bit node control memory, and one differential optical transmitter. The five stages of node arrays are interconnected to form a two-dimensional banyan network by the use of Fourier-plane computer-generated holograms. System input and output are made by two-dimensional fiber-bundle matrices, and the system optical hardware design incorporates frequency-stabilized lasers, pupil-division beam combination, and a hybrid micro-macro lens for fiber-bundle imaging. Optomechanical packaging of the system ut lizes modular kinematic component positioning and active thermal control to enable simple rapid assembly. Two preliminary operational experiments are completed. In the first experiment, five stages are operated at 50 Mbits/s with 15 active inputs and outputs. The second experiment attempts to operate two stages of second-generation node arrays at 155 Mbits/s, with eight of the 15 active nodes functioning correctly along the straight switch-routing paths.

Beam array generation and holographic interconnections in a free-space optical switching network.

Free-space photonic switching systems that optically interconnect large arrays of simple processing elements have already been demonstrated [IEEE Photon. Technol. Lett. 2, 438,600 (1990); Appl. Opt. 31, 5431 (1992); Electron. Lett. 27, 1869 (1991)]. In these system experiments, diffractive optical elements served as critical components that provided functionality not easily assumed by conventional optics. In the latest optical switching network, binary phase gratings were used to generate arrays of uniformintensity beams to illuminate modulators in the processor array. In addition, space-invariant binary phase grating designs were integral in forming the Banyan interconnection network used to link arrays in the system. Here we discuss the function, design, and performance of these diffractive elements.

Six-stage digital free-space optical switching network using symmetric self-electro-optic-effect devices.

We describe the design and demonstration of an extended generalized shuffle interconnection network, centrally controlled by a personal computer. A banyan interconnection pattern is implemented by use of computer-generated Fourier holograms and custom metallization at each 32 × 32 switching node array. Each array of electrically controlled tristate symmetric self-electro-optic-effect devices has 10,240 optical pinouts and 32 electrical pinouts, and the six-stage system occupies a 9 in. × 12.5 in. (22.9 cm × 31.7 cm) area. Details of the architecture, optical and mechanical design, and system alignment and tolerancing are presented.

Design and analysis of a bidirectional free-space photonic switch based on the ALOHA scheme.

A bidirectional multichannel photonic switching architecture based on the ALOHA multiuser scheme is presented and analyzed. An implementation of the broadcasting hardware, which uses free-space digital optics and fiber-bundle arrays, is described. The advantages and disadvantages of such an implementation are outlined, and the throughput and delay performance of it are analyzed and compared to other architectures. Our investigation shows that the switching capacity of such an architecture grows at least linearly in the number of channels.

Analysis of control subsystems for free-space photonic switching architectures.

Four different methods of injecting control signals into photonic switches are compared. A control injection model based on time-division-multiplexed switching is developed, and the analysis studies the effects of the different control injection schemes on network performance, system complexity, and system packaging. Serious system-level limitations are identified for all the control injection schemes in switching networks with high reconfiguration rates.

Experimental investigation of a free-space optical switching network by using symmetric self-electro-optic-effect devices.

A prototype digital free-space photonic switching fabric is demonstrated. It consists of three cascaded 16 x 8 arrays of symmetric self-electro-optic-effect devices that are used as logic gates that implement part of a multistage interconnection network. We discuss architecture, device tolerancing, optical system design, and optomechanical design. This optical circuit is successfully configured as a fully operational array of 32 independent 2 x 2 nodes and operates at 100 kHz.

Free-space photonic switching architectures based on extended generalized shuffle networks.

A new class of networks that is well suited for free-space photonic switching applications is described. These networks are known as extended generalized shuffle networks. It is shown that these networks can provide low blocking probabilities while requiring low hardware costs. In fact, if sufficient hardware is added to these networks, they become strictly nonblocking networks (with blocking probabilities equal to zero). The hardware cost of an extended generalized shuffle network can be modified to yield any desired blocking probability, so cost-effective designs are possible. In addition, it is shown that these networks are extremely fault tolerant, and they can also be designed to have high system availabilities. Because the networks can use various types of interconnections to connect the nodes and because the nodes can have various types of functionality, these networks also provide high degrees of flexibility that can be used to optimize a free-space photonic design. The design of extended generalized shuffle networks based on a particular node type that is easy to implement with symmetric self-electro-opticeffect devices is studied.

Photonic switching applications of 2-D and 3-D crossover networks based on 2-input, 2-output switching nodes.

Optical implementations of both 2-D and 3-D crossover networks are described, and we show that these networks can be used for connecting multiple stages of 2-input, 2-output switching elements. We also show that simple conversion steps can be used to convert 2-D crossover networks into 3-D crossover networks. Both network types can be implemented with low loss optical imaging systems, and we show that the same optics can be used to implement the intranode connections and the internode for various types of 2-input, 2-output switching elements. In addition, we discuss the difficulties that arise when the same optical hardware is applied to switching elements of larger dimensionality.

Self-routing crossbar packet switch employing free-space optics for chip-to-chip Interconnections.

A nonblocking crossbar network that employs free-space optical interconnections between optoelectronic switching nodes is proposed. The architecture can be implemented using standard electronic technologies for the switching logic, systematic self-electro-optic effect devices for modulators and detectors, and fairly simple optics to connect adjacent chips in the network. Since optical interconnections are only required between adjacent chips, this architecture may have advantages compared with other architectures that have been proposed using optical interconnections between electronic chips. In addition, a simple routing scheme is discussed that permits the optical crossbar network to be operated as a self-routing packet switch. This packet switch provides for contention resolution, priority routing, and automatic increases in the priority of blocked packets. An example illustrating one implementation of the network is then described and analyzed.

Quantum well optical tri-state devices.

We demonstrate quantum well tri-state logic devices for possible use in optical bus architectures. These optical devices are analogous to the tri-state devices often used in electronic buses, where each device can be actively on, actively off, or disabled with at most one device on the bus active at a time. We show two methods of generating these tri-state data, one using tri-state quantum well modulators and one using optical tri-state self-electrooptic effect devices, and we demonstrate a simple optical bus consisting of two such devices. Finally, we comment on the limitations on the number of devices that can be connected to a bus of this type.

Free-space optical implementation of a feed forward crossbar network.

The crossbar network has been a popular topology for proposed guided wave optical switching systems as well as for proposed free-space optical switching and computing systems. However, these crossbar system proposals suffer from fundamental problems that may limit the overall size of the network. A new implementation of a free-space optical crossbar network (the feed forward crossbar network) is proposed which may be able to overcome these problems. One-dimensional and two-dimensional implementations are described. The resulting optical interconnections in both implementations are space-invariant interconnections, so the optical hardware requirements are minimal.

Topological equivalence of optical crossover networks and modified data manipulator networks.

The crossover network is a multistage interconnection network that shows potential for use in optical computing and photonic switching applications. In this paper, a proof of topological equivalence between the crossover network and the modified data manipulator network is presented. It is shown that the Gray Code can be used as the mapping function between the crossover network and a network which is equivalent to the modified data manipulator network. Given the results of this proof, the optical crossover network can then be proposed as the optical interconnection fabric for many switching and computing applications.

Optical design of a digital switch.

An optical design of a time multiplexed nonblocking space switch is described for optically nonlinear arrays of logic devices interconnected in free space. Regular interconnects in the form of crossovers are used for interconnecting optical logic devices, and some efficiency is lost due to the strict use of regular interconnects. It is shown that for this application, the higher component count is comparable with the component count for the electronic implementation of the switch. We maintain that for a high bandwidth application such as packet switching, simple bulk optics provides a suitable medium for interconnecting optical logic devices even at high speeds, and that a more elaborate approach is not warranted.

Performance analysis of optical symbolic substitution.

Symbolic substitution is being considered for use in several optical processing systems. Two fundamentally different architectures that implement symbolic substitution will be studied. A typical application (N-bit binary addition) is chosen as a benchmark for system level performance, and the strengths and weaknesses of several implementations of these two architectures are identified and compared.