Guided-wave multiwavelength polarization-insensitive processing module for a parallel multicomparand perfect-match algorithm.

We present a design for a planar guided-wave polarization-insensitive (intensity-based) optoelectronics module that provides a parallel perfect-match search for database and text processing. The module is based on a content-addressable memory model for parallel information retrieval. We propose the use of planar guided-wave optics with multiwavelength processing to achieve a substantially high degree of performance and parallelism. Based on initial performance analysis, the proposed module is capable of achieving an aggregate processing speed of 10(12) bits/s.

Architectural approach to the role of optics in monoprocessor and multiprocessor machines.

The relevance of introducing optical interconnects (OI's) in monoprocessors and multiprocessors is studied from an architectural point of view. We show that perhaps the major explanation for why optical technologies have nearly been unable to penetrate into computers is that OI's generally do not shorten the memory-access time, which is the most critical issue for today's stored-program machines. In monoprocessors the memory-access time is dominated by the electronic latency of the memory itself. Thus implementing OI's inside the memory hierarchy without changing the memory architecture cannot dramatically improve the global performance. In strongly coupled multiprocessors the node-bypass latency dominates. Therefore the higher the connectivity (possibly with optics), the shorter the path to another node, but the more expensive the network and the more complex the structure of electronic nodes. This relation leaves the choice of the best network open in terms of simplicity and latency reduction. The bottlenecks resulting from and the benefits of implementing OI's are discussed with respect to symmetric multiprocessors, rings, and distributed shared-memory supercomputers.

Equivalency-processing parallel photonic integrated circuit (EP3IC): equivalence search module based on multiwavelength guided-wave technology.

We present an optoelectronic module called the equivalency-processing parallel photonic integrated circuit (EP(3)IC) that is created specifically to implement high-speed parallel equivalence searches (i.e., database word searches). The module combines a parallel-computation model with multiwavelength photonic integrated-circuit technology to achieve high-speed data processing. On the basis of simulation and initial analytical computation, a single-step multicomparand word-parallel bit-parallel equality search can attain an aggregate processing speed of 82 Tbit/s. We outline the theoretical design of the monolithic module and the integrated components and compare this with a functionally identical bulk-optics implementation. This integrated-circuit solution provides relatively low-power operation, fast switching speed, a compact system footprint, vibration tolerance, and ease of manufacturing.

Multiwavelength optical content-addressable parallel processor for high-speed parallel relational database processing.

We present a novel, to our knowledge, architecture for parallel database processing called the multiwavelength optical content-addressable parallel processor (MW-OCAPP). The MW-OCAPP is designed to provide efficient parallel data retrieval and processing by means of moving the bulk of database operations from electronics to optics. It combines a parallel model of computation with the many-degrees-of-processing freedom that light provides. The MW-OCAPP uses a polarization and wavelength-encoding scheme to achieve a high level of parallelism. Distinctive features of the proposed architecture include (1) the use of a multiwavelength encoding scheme to enhance processing parallelism, (2) multicomparand word-parallel bit-parallel equality and magnitude comparison with an execution time independent of the data size or the word size, (3) the implementation of a suite of 11 database primitives, and (4) multicomparand two-dimensional data processing. The MW-OCAPP architecture realizes 11 relational database primitives: difference, intersection, union, conditional selection, maximum, minimum, join, product, projection, division, and update. Most of these operations execute in constant time, independent of the data size. We outline the architectural concepts and motivation behind the MW-OCAPP's design and describe the architecture required for implementing the equality and intersection-difference processing cores. Additionally, a physical demonstration of the multiwavelength equality operation is presented, and a performance analysis of the proposed system is provided.

All-optical crossbar switch using wavelength division multiplexing and vertical-cavity surface-emitting lasers.

A design for an all-optical crossbar network utilizing wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) technology and a combination of free-space optics and compact optical waveguides is presented. Polymer waveguides route the optical signals from a spatially distributed array of processors to a central free-space optical crossbar, producing a passive, all-optical, fully connected crossbar network directly from processor to processor. The analyzed network could, relatively inexpensively, connect local clusters of tightly integrated processors. In addition, it is also believed that such a network could be extended, with wavelength reuse, to connect much larger numbers of processors in a multicluster network.

Optical implementation of a constant-time multicomparand bit-parallel magnitude-comparison algorithm using wavelength- and polarization-division multiplexing with application to parallel database processing.

We present a word- and bit-parallel magnitude-comparison architecture that permits multiple comparands to be compared with multiple relations in constant time. The proposed magnitude-comparison algorithm uses a novel polarization and wavelength-encoding scheme to achieve a fast, scalable realization. Distinctive features of the proposed architecture include (1) the use of a multiple-wavelength encoding scheme to increase processing parallelism and (2) multiple-comparand word- and bit-parallel comparison with an execution time that is independent of the data or word size.

Hierarchical optical ring interconnection (HORN): scalable interconnection network for multiprocessors and multicomputers.

A new interconnection network for massively parallel computing is introduced. This network is called a hierarchal optical ring interconnection (HORN). The HORN consists of a single-hop, scalable, constant-degree, strictly nonblocking, fault-tolerant interconnection topology that uses wavelength-division multiple access to provide better utilization of the terahertz bandwidth offered by optics. The proposed optical network integrates the attractive features of hierarchical ring interconnections, e.g., a simple node interface, a constant node degree, better support for the locality of reference, and fault tolerance, with the advantages of optics. The HORN topology is presented, its architectural properties are analyzed, and an optical design methodology for it is described. Furthermore, a brief feasibility study of the HORN is conducted. The study shows that the topology is highly amenable to optical implementation with commercially available optical elements.

Incrementally scalable optical interconnection network with a constant degree and constant diameter for parallel computing.

A new scalable interconnection topology called the spanning-bus connected hypercube (SBCH) that is suitable for massively parallel systems is proposed. The SBCH uses the hypercube topology as a basic building block and connects such building blocks by use of multidimensional spanning buses. In doing so, the SBCH combines positive features of both the hypercube (small diameter, high connectivity, symmetry, simple routing, and fault tolerance) and the spanning-bus hypercube (SBH) (constant node degree, scalability, and ease of physical implementation), while at the same time circumventing their disadvantages. The SBCH topology permits the efficient support of many communication patterns found in different classes of computation, such as bus-based, mesh-based, and tree-based problems, as well as hypercube-based problems. A very attractive feature of the SBCH network is its ability to support a large number of processors while maintaining a constant degree and a constant diameter. Other positive features include symmetry, incremental scalability, and fault tolerance. An optical implementation methodology is proposed for the SBCH. The implementation methodology combines the advantages of free-space optics with those of wavelength-division multiplexing techniques. An analysis of the feasibility of the proposed network is also presented.

Feasibility study of a scalable optical interconnection network for massively parallel processing systems.

The theoretical modeling of a novel topology for scalable optical interconnection networks, called optical multimesh hypercube (OMMH), is developed to predict size, bit rate, bit-error rate, power budget, noise, efficiency, interconnect distance, pixel density, and misalignment sensitivity. The numerical predictions are validated with experimental data from commercially available products to assess the effects of various thermal, system, and geometric parameters on the behavior of the sample model. OMMH is a scalable network architecture that combines positive features of the hypercube (small diameter, regular, symmetric, and fault tolerant) and the mesh (constant node degree and size scalability). The OMMH is implemented by a free-space imaging system incorporated with a space-invariant hologram for the hypercube links and fiber optics to provide the mesh connectivity. The results of this work show that the free-space links can operate at 368 Mbits/s and the fiber-based links at 228 Mbits/s for a bit-error rate of 10(-17) per channel. The predicted system size for 32 nodes in the OMMH is 4.16 mm × 4.16 mm × 3.38 cm. Using 16-bit, bit-parallel transmission per node, the system can operate at a bit rate of up to 5.88 Gbits/s for a size of 1.04 cm × 1.04 cm × 3.38 cm.

Experimental demonstration of the optical multi-mesh hypercube: scaleable interconnection network for multiprocessors and multicomputers.

A prototype of a novel topology for scaleable optical interconnection networks called the optical multi-mesh hypercube (OMMH) is experimentally demonstrated to as high as a 150-Mbit/s data rate (2(7) - 1 nonreturn-to-zero pseudo-random data pattern) at a bit error rate of 10(-13)/link by the use of commercially available devices. OMMH is a scaleable network [Appl. Opt. 33, 7558 (1994); J. Lightwave Technol. 12, 704 (1994)] architecture that combines the positive features of the hypercube (small diameter, connectivity, symmetry, simple routing, and fault tolerance) and the mesh (constant node degree and size scaleability). The optical implementation method is divided into two levels: high-density local connections for the hypercube modules, and high-bit-rate, low-density, long connections for the mesh links connecting the hypercube modules. Free-space imaging systems utilizing vertical-cavity surface-emitting laser (VCSEL) arrays, lenslet arrays, space-invariant holographic techniques, and photodiode arrays are demonstrated for the local connections. Optobus fiber interconnects from Motorola are used for the long-distance connections. The OMMH was optimized to operate at the data rate of Motorola's Optobus (10-bit-wide, VCSEL-based bidirectional data interconnects at 150 Mbits/s). Difficulties encountered included the varying fan-out efficiencies of the different orders of the hologram, misalignment sensitivity of the free-space links, low power (1 mW) of the individual VCSEL's, and noise.

Generalized methodology for modeling and simulating optical interconnection networks using diffraction analysis.

Research in the field of free-space optical interconnection networks has reached a point where simulators and other design tools are desirable for reducing development costs and for improving design time. Previously proposed methodologies have only been applicable to simple systems. Our goal was to develop a simulation methodology capable of evaluating the performance characteristics for a variety of different free-space networks under a range of different configurations and operating states. The proposed methodology operates by first establishing the optical signal powers at various locations in the network. These powers are developed through the simulation by diffraction analysis of the light propagation through the network. After this evaluation, characteristics such as bit-error rate, signal-to-noise ratio, and system bandwidth are calculated. Further, the simultaneous evaluation of this process for a set of component misalignments provides a measure of the alignment tolerance of a design. We discuss this simulation process in detail as well as provide models for different optical interconnection network components.

Design of an optical content-addressable parallel processor for expert systems.

The slow execution speed of current rule-based systems (RBS's) has restricted their application areas. To improve the speed of RBS's, researchers have proposed various electronic multiprocessor systems as well as optical systems. However, the electronic systems still suffer in performance from the large amount of required time-consuming pattern-matching and comparison operations at the core of RBS's. And optical systems do not fully exploit the available parallelism in RBS's. We propose an optical content-addressable parallel processor for expert systems. The processor executes the three basic RBS operations, match, select, and act, in a highly parallel fashion. Additionally, it extracts and exploits all possible parallelism in a RBS. Distinctive features of the proposed system include the following: (1) two-dimensional representation of data (knowledge) and control information to exploit the parallelism of optics in the three RBS units; (2) capability of processing general-domain knowledge expressed in terms of variables, numbers, symbols, and comparison operators such as greater than and less than; (3) the parallel optical match unit, which performs the two-dimensional optical pattern matching and comparison operations; (4) a novel conflict-resolution algorithm to resolve conflicts in a single step within the optical select unit. The three units and the general-knowledge representation scheme are designed to make the optical content-addressable parallel processor for expert systems suitable for any high-speed general-purpose RBS.

Constant-time parallel sorting algorithm and its optical implementation using smart pixels.

Sorting is a fundamental operation that has important implications in a vast number of areas. For instance, sorting is heavily utilized in applications such as database machines, in which hashing techniques are used to accelerate data-processing algorithms. It is also the basis for interprocessor message routing and has strong implications in video telecommunications. However, high-speed electronic sorting networks are difficult to implement with VLSI technology because of the dense, global connectivity required. Optics eliminates this bottleneck by offering global interconnects, massive parallelism, and noninterfering communications. We present a parallel sorting algorithm and its efficient optical implementation. The algorithm sorts n data elements in few steps, independent of the number of elements to be sorted. Thus it is a constant-time sorting algorithm [i.e., O(1) time]. We also estimate the system's performance to show that the proposed sorting algorithm can provide at least 2 orders of magnitude improvement in execution time over conventional electronic algorithms.

Optical binary de Bruijn networks for massively parallel computing: design methodology and feasibility study.

The interconnection network structure can be the deciding and limiting factor in the cost and the performance of parallel computers. One of the most popular point-to-point interconnection networks for parallel computers today is the hypercube. The regularity, logarithmic diameter, symmetry, high connectivity, fault tolerance, simple routing, and reconfigurability (easy embedding of other network topologies) of the hypercube make it a very attractive choice for parallel computers. Unfortunately the hypercube possesses a major drawback, which is the complexity of its node structure: the number of links per node increases as the network grows in size. As an alternative to the hypercube, the binary de Bruijn (BdB) network has recently received much attention. The BdB not only provides a logarithmic diameter, fault tolerance, and simple routing but also requires fewer links than the hypercube for the same network size. Additionally, a major advantage of the BdB network is a constant node degree: the number of edges per node is independent of the network size. This makes it very desirable for large-scale parallel systems. However, because of its asymmetrical nature and global connectivity, it poses a major challenge for VLSI technology. Optics, owing to its three-dimensional and globalconnectivity nature, seems to be very suitable for implementing BdB networks. We present an implementation methodology for optical BdB networks. The distinctive feature of the proposed implementation methodology is partitionability of the network into a few primitive operations that can be implemented efficiently. We further show feasibility of the presented design methodology by proposing an optical implementation of the BdB network.

Modeling and simulation methodology for digital optical computing systems.

A modeling and simulation methodology for digital optical computing systems is introduced in this paper. The methodology predicts maximum performance of a given optical computing architecture and evaluates its feasibility. As an application example, we apply this methodology to evaluate the feasibility and performance of the optical content-addressable parallel processor proposed in Appl. Opt. 31, 3241 (1992). The approach consists of two major phases. The first phase involves analytical studies of the effects of design parameters such as cross talk, diffraction-limited beam spot diameter, and pitch on system performance parameters such as signal packing density and skew time. In the second phase, a simulation model and a simulator are introduced by the use of GLAD (General Laser Analysis and Design, an optical software package developed by Applied Optics Research) to evaluate the combined effects of bit-error rate, bit rate, optical power efficiency, available source power, and signal contrast on the perfor ance parameters such as signal packing density, misalignment tolerance, and distance between devices. The methodology presented here investigates the model, not on a component-by-component basis, but as a whole, which produces a more realistic representation of the actual laborator prototype. The proposed methodology is intended to reduce the optical computing system design time as well as the design risk associated with building a prototype system.

Scalable optical hypercube-based interconnection network for massively parallel computing.

Two important parameters of a network for massively parallel computers are scalability and modularity. Scalability has two aspects: size and time (or generation). Size scalability refers to the property that the size of the network can be increased with nominal effect on the existing configuration. Also, the increase in size is expected to result in a linear increase in performance. Time scalability implies that the communication capabilities of a network should be large enough to support the evolution of processing elements through generations. A modular network enables the construction of a large network out of many smaller ones. The lack of these two important parameters has limited the use of certain types of interconnection networks in the area of massively parallel computers. We present a new modular optical interconnection network, called an optical multimesh hypercube (OMMH), which is both size and time scalable. The OMMH combines positive features of both the hypercube (small diameter, high connectivity, symmetry, simple routing, and fault tolerance) and the torus (constant node degree and size scalability) networks. Also presented is a three-dimensional optical implementation of the OMMH network. A basic building block of the OMMH network is a hypercube module that is constructed with free-space optics to provide compact and high-density localized hypercube connections. The OMMH network is then constructed by the connection of such basic building blocks with multiwavelength optical fibers to realize torus connections. The proposed implementation methodology is intended to exploit the advantages of both space-invariant free-space and multiwavelength fiber-based optical interconnect technologies. The analysis of the proposed implementation shows that such a network is optically feasible in terms of the physical size and the optical power budget.

Optical content-addressable parallel processor for high-speed database processing.

We extend the concept of optical content-addressable parallel processing [Appl. Opt. 31, 3241 (1992)] to a novel architecture designed specifically for the parallel and high-speed implementation of database operations called optical content-addressable parallel processor for relational database processing (OCAPPRP). An OCAPPRP combines a parallel model of computation, associative processing, with parallel and high-speed technology optics. The architecture is developed to provide optimal support for high-speed parallel equivalence (pattern matching) and relative-magnitude searches (greater than and lesser than). Distinctive features of the proposed architecture include (1) a two-dimensional match-compare unit for two-dimensional pattern matching, (2) constant-time retrieval of database entries, (3) an optical word and bit-parallel relative-magnitude single-step algorithm, and (4) the capability of constanttime sorting. Since relational database operations rely heavily on parallel equivalence or relativemagnitue searches, database processing is an excellent candidate for implementation on an OCAPPRP. The architecture delivers a speedup factor of n over conventional optical database architectures, where n is the number of rows in a database table. We present an overview of the architecture followed by its optical implementation. The representative relational database operations, intersection, and selection are outlined to illustrate the architecture's potential for efficiently supporting high-speed database processing.

Optical implementation of a single-iteration thresholding algorithm with applications to parallel data-base/knowledge-base processing.

Threshold (or relative magnitude) search is traditionally performed iteratively in a bit-serial manner in optical data-base/knowledge-base machines, which results in an execution time proportional to the operand size. We present a single-step threshold search algorithm and its optical implementation. The proposed algorithm performs magnitude comparison in constant time, independent of the operand size, and consequently it greatly increases the performance of optical data-base/knowledge-base processing operations such as searching, selection, retrieving, and sorting.

Parallel electro-optical rule-based system for fast execution of expert systems.

The slow execution speed of current rule-based systems has restricted their application areas. Multiprocessor architectures have been proposed to overcome this limitation. However, as the number of processors in a multiprocessor system grows, so does the cost of communication between processors or between processor and memory units. The use of optics for a fast and parallel implementation of rule-based systems is proposed. The proposed optical system is hybrid in nature, using electronics for the user interface and optics for the rule-based inference engine. The proposed system uses twodimensional planes as basic computational entities and is therefore able to provide concurrent rule processing. Furthermore, it provides highly efficient implementation of the basic operations needed in rule-based systems; namely, matching, selection, and rule firing. The execution speed of the proposed system is theoretically estimated and is shown to be potentially of orders of magnitude faster than current electronic system.