We have designed and fabricated PIN photodiode based ROSA used for FTTX applications. The critical nonlinearity parameters of Inter-modulation Distortion (IMD) were measured by two RF modulated light sources near 1550nm wavelength channels. A cost effective measuring system with narrow pass band filter was set up and some procedures were utilized for determining the low level signals of IMD. Obtained test results were used in real time to guide packaging process to achieve best receiver performance.
We describe a cost-effective new packaging platform for CWDM passives. The Compact CWDM (CCWDM) devices use free-space beam cascading schemes and offer far better size, performance and reliability measures than traditional counterparts built by cascading 3-port thin-film filters.
Reconfigurable optical add/drop multiplexer (ROADM) is a next generation critical component that facilitates the
network system evolution from a point-to-point transmission-oriented structure to an all-optical, wavelength-flexible,
dynamic network. ROADM enables flexible removal and insertion of WDM channels at either a head-end or
intermediate nodes-making it possible for true network provisioning and reconfiguration.
We will review the pros and cons of each of the techniques for tunable OADM, from their operating principles to their
practical implementations with special emphasis on two approaches: a TTF based three-port tunable filter as a basic
one-channel tunable add/drop multipexer and a full-scale, MEMS mirror array based 80-channel reconfigurable OADM
subsystem. Comparative laboratory experimental results with theoretical calculations are presented.
In order to reduce size and cost, and at the same time increase overall performance, we designed a compact 8-ch CWDM MUX/DeMUX scheme based on free space optics. The device offers the following competitive performance specifications: IL < 0.8dB, IL ripple < 0.2dB, PDL < 0.1dB, PMD < 0.15ps, CD < 3ps/nm, IL uniformity < 0.3dB, adjacent channel isolation > 40dB, return loss > 50dB and pass-band bandwidth > 14nm. Such a device can operate in the temperature range of -10C° to 70C° with a TDL ~0.002dB/C°. In this paper, we will discuss the following three critical aspects of its design and implementation: (I) Design considerations and tolerance simulation. Here we discuss optimization of a set of critical design parameters: angle of incidence (AOI), beam size (BS), working distance (WD), filter aperture, filter orientation and filter-to-filter distance. (II) Build-in tolerance and critical alignment control. We have done extensive simulations to identify the critical variables and tolerance range for each variable. Based on this analysis, we then built in the alignment guidance and tolerances control into mechanical design. (III) Process control, material selection and surface preparation: Here we discuss the proper usage of the adhesives including the types of dual-effect adhesives, use of silica filler and coupling agent, surface preparation to achieve proper surface energy, tension and porosity, the optimum combination of the substrate and adhesive material for best shear and peel strength, and balancing temperature compensation and stress absorption.
Reconfigurable Add/drop Multiplexer (ROADM) is a broad definition of a functionally reconfigurable filtering device for dynamic networking. We focus on a class of ROADM architecture that allows scalability of wavelength channels, add/drop port counts as well as functional capability of integrating variable attenuation and monitoring elements. We demonstrate the proposed concepts of integrating a ROADM with a variable optical attenuator and a performance monitor array.
We discuss recent surge of interests in coarse DWM (CWDM) applications and implied challenges for low cost and compact devices. We show that for further cost-reduction and performance enhancements, an old WDM packaging architecture can be revitalized to address the new compact CWDM (CCWDM) filter challenges. In particular, we demonstrate a CCWDM filter platform and show its use in both an 8-channel Mux/DeMux and a 4-channel OADM applications.
We describe a nonlinearly chirped fiber Bragg grating (FBG) based multichannel device that can perform tunable chromatic dispersion compensation. Complex or phase only sampling allows a single grating to operate on multiple DWDM channels. Various key performance parameters are discussed.
We introduce a new integrated solid-optics component, a X- cube, which can perform lossless beam-splitting and filtering functionality among four input beams. The X-cube can also be used for various wavelength-division multiplexing-based communication and interconnection applications, such as star-coupling, wavelength routing, and add/drop multiplexing. Our demonstrated fiber-interfaces X- cube opto-mechanical packaging shows an insertion loss of 2.1 dB, a uniformity ratio of 1.036 with a uniformity variance of 0.279.
Bandwidth incompatibility between a central processing unit (CPU) and printed circuit board (PCB) within a computer system has been a long noted problem. Physics and material sciences suggest that the problem could become worse before getting solved. This is fundamentally due to nature of propagation of electric signals in very large scale integration of conductive wires. The market has witnessed a rapid increase in chip level clock frequency (for a mainstream PC) from 100 MHz few years ago to 800 MHz nowadays. The PC bus bandwidth, however, for the same time span, grew only from 33 MHz to 100 MHz. Although the widely anticipated adoption of 133 MHz is on its way, any serious technical challenges remain. Such a large magnitude of bandwidth discrepancy between the chip and board levels has prompted Intel Corp. to aggressively invest into various technologies to increase speed at board level so that the performance of its future generation of faster and more powerful CPU chips can be effectively utilized. Rambus, Inc. with a strong backing from Intel has come up with a faster memory bus technology that can increase the bus speed several times. Competitions from sampling a data bus at both clock signal edges using the so-called double data rate (DDR) technology are also making their strides. However, high-speed electric signals in densely packed conductive wiring structures inevitably generate the so-called electromagnetic interference among each others. Tougher challenges lie ahead for future generations of large bandwidth interconnect technology at the board level.
We discuss needs for using large-bandwidth, EMI-free optical interconnects inside computer systems and why the back-plane is the first possibility of applying optical technology. We compare free-space and guided-wave optical solutions for various fundamental and practical measures and show our conclusion that 2D data-capable guided wave optical channels can offer most competitive solutions. We capitalize on various unique advantages that a polymer optical fiber offers and propose to combine such fibers and embedding techniques we developed to deliver reliable optical channels on conventional printed circuit boards and back-planes. We show that an embedded polymer fiber opticaldistribution circuit can effectively deliver low-loss and high uniformity clock data up to 10Gb/s. We extend the concept of embedding to the multi-layer point-to-point 2D parallel optical back-plane. To further extend the capability of these optical data highways to incorporate data-sharing functionality, compact and integrated free-space optical components are proposed to serve as image-splitting devices. We discuss various recent experiments in our lab and present several demonstration prototypes during our presentation.
Cross-connect switching is a common switching architecture for telecom and datacom applications. Large bandwidth O-E interface devices have recently been made commercially available. Small scale fast electronic switches and large scale optical interconnect circuits can be effectively used for handling large bandwidth O-E cross-connect switching. In this paper, we show two packaged and connectorized optical interconnect circuits. The first one is a 100 X 100 channel guided-wave circuit fully compatible, through MT array connectors, to O-E interface devices, such as Motorola OPTOBUSTM or Simens PAROLITM chips. The second one is a more scalable architecture which is a hybrid of free- space and fiber circuits. For demonstration purpose, a 256 X 256 channel hybrid circuit is shown. Key parameters, such as insertion loss, cross-talk, and bit-error-rate of these interconnect circuits are presented. Transmission and routing of video data are performed to demonstrate interconnect quality of various data links. Scalability of these demonstrated circuits to larger sizes are speculated.
We propose star-coupling based on large-core polymer optical fibers. Mixing rods with tapered and untapered ends are employed to form 1 X 7 and 7 X 7 broadcast and mixing couplers. We found that excess loss and coupling uniformity are mixing length dependent and that of a 15 cm length tapered mixing-rod based 1 X 7 coupler can have a 1.72 dB excess loss and a 1.0 dB uniformity. The average excess loss and uniformity for a constructed 18 cm mixing-rod length 7 X 7 star-coupler are found to be 1.38 dB and 1.92 dB, respectively.
We describe a polymer fiber image guided (PFIG)-based optical interconnect circuits which incorporates add/drop capabilities. 2D array data transmitting in segments of PFIG's can be inserted and taken away at various free-space add/drop nodes between these segments. The add/drop nodes are implemented using free-space mini-optical components. A 4-node hybrid circuits using PFIG's to transmit bit-parallel data and free-space components to perform add/drop is experimentally demonstrated. Various power and resolution measurements of the implemented systems are presented.
Cross-connect switch is a popular switching architecture for telecom and datacom applications. Using various switching components and a k-shuffle interconnect, a cross-connect switch can be configured for general-purpose, blocking as well as non-blocking networking applications. We show that a 1D k-shuffle interconnect pattern is topologically equivalent to a 2D transposition transform pattern. Based on this observation and using space-invariant optical components, the transposition transform interconnect is experimentally implemented. To achieve a sensible packing, we propose to incorporate fiber arrays into the implementation so that the interconnect offers connectorized plug-and-play capability with its switching arrays. Experimental results of implementing a 256 X 256 connectorized free-space and fiber hybrid transposition transform interconnect for cross-connect switching are presented. Key parameters, such as insertion loss, cross- talk, and bit-error-rate of the hybrid interconnect module are measured. Video data are used to demonstrate interconnect quality of various link channels. Scalability to larger interconnects are speculated.
We propose to implement a modularly structured planar wave- guiding star-coupler for large-core polymer fiber-based optical interconnect applications. An 8 X 8 version of the coupler is demonstrated using polymer materials. The planar star-coupler can be mass-produced using injection molding technology at substantially low cost. Measurements indicate that by properly working out a trade-off between device compactness, uniformity and coupling efficiency, a < 2.0 dB power fluctuation among all receiving channels and a 3.1 dB excess power loss are obtainable.
We review recent progresses in various POF related optical interconnect projects at NEC Research Institute. These projects were initiated to study cost-effective sub-local optical interconnect solutions that can potentially compete with copper-based solutions in future. The projects include both coupling schemes for networking various POF data links, and point-to-point polymer circuits which can route data in both serial and parallel formats. Many of the mentioned projects are still on-going and thus the report here has the nature of progress update.
A fully packaged opto-electronic cross-connect interconnect fiber circuit for data communication applications is demonstrated. Using bit-parallel optical link technology, the circuit offers EO and OE conversion capability, as well as 100 X 100 cross-connectivity. Using this technology together with an array of 10 X 10 digital electronic switches, fast cross-connect switches of the scale of 100 X 100 can be implemented. The insertion loss of the compact 100 X 100 cross-connect interconnect circuit ranges from 0.4 dB to 2.9 dB among all possible connections. Optical transmissions with bit-error-rate of < 10-12 can be maintained at near 1 Gb/s channel bandwidth when the circuit is powered by the OPTOBUS chips. The system is expected to have an aggregated interconnect bandwidth near 100 Gb/s when being fully connected with the OPTOBUS chips.
We demonstrate an OPTOBUS-based opto-electronic cross- connector. The maximum optical insertion loss of the compact 100 X 100 cross-connect box was measured to be 2.8 dB. BER of < 10-12 can be maintained at 900 Mb/s per channel bandwidth.
Embedding of end-tapered, thin-cladding fiber bundles for board- level large bandwidth optical clock distribution is proposed and implemented. Fan-outs of 1 to 64- and 128-nodes on a printed circuit board of area 13 X 9 cm2 are experimentally demonstrated. Dispersion measurement shows a 30 picosecond pulse broadening over 30 cm length of the fiber, thereby indicating multi Gb/s clock delivery capability. Power coupling efficiency of 3 dB with coupling nonuniformity of 4.7 - 5.5 dB is observed.
In this paper, in order to properly promote usage's of optics for future interconnection applications, we revisit some fundamental physics governing light propagation in linear media. In particular, we wish to address how the point-topoint data communication capacity is related to the degree of freedom (DOF) of optics, and how packaging and other constraints limit the DOF of optics for exercising its power of interconnections. We hope that a correct understanding of the fundamentals of optics for interconnections can help maximize its advantages while bypassing its drawbacks.
As fiber optics becomes a standard means of transmitting long haul telecommunication signals. costs of adopting fiber solutions for various other communication applications steadily decrease. Optics starts to challenge copper-based solutions in many short-distance data communication domains. Recent progress in developing vertical -cavity surlaceemitting lasers (VCSEL) has lead to a belief that a proper combination of the VCSEL and fibers can provide a cost-effective solution to many bandwidth-demanding local data communication bottleneck problems. A trend to develop VCSEL-hased fiber optic parallel data links has been witnessed [1-2]. Among the most notable approaches are the parallel fiber link prolect by the Opto-electronic Technology Consortium (OETC) . the Optobus project by the Motorola Corp [21. These, along with many other similar, approaches feature 1D array of bit-parallel connections of optical data between a ID VCSEL array and a ID photodetector array. A lD fiber ribbon containing various fiber channels is used as flexible parallel data channels. As demand for bandwidth rapidly increases, wider and wider 1D ribbons containing more and more parallel channels are being proposed. To cope with future bandwidth demand, a direct extension of the 1D approach to a 2D form has also been studied. 2D VCSEL arrays are under development. Methods of fabricating small 2D arrays of individual fibers are being explored [341. It was noted that unless active alignment methods are successfully developed, it is difficult to control core pitch fluctuations of such a fiber array. A somewhat different 2D approach was recent proposed . It uses a fiber image guide (FIG) which contains a large number of closely packed fibers to transmit the image of the VCSEL to the other side. A FIG simply images between a 2D input and output arrays. Among mentioned advantages of this approach are its capability to transmit a scalpel number of parallel channels and its relaxed alignment condition. In this talk, we quantitatively study various interface problems this FIG-based approach may experience and try to understand its capabilities and limitations.
Optical signal distributions through side-emitting ports along a polymer optical fiber are demonstrated using etched micro-mirrors. Low-cost serial and parallel mirror fabrication processes are described. Near uniform light distributions through as many as 200 such output ports along a single fiber of 0.75 mm diameter and 0.485 numerical aperture are obtainable. A 4 X 16 plastic array coupler for fiber-to-fiber interconnections was fabricated. The fabricated couplers have maximum coupling efficiencies of up to 84.7% and 91.4% using, respectively, the total internal reflection type and metal coating type micro-mirrors. The coupling uniformity for the two cases are 84% and 76%, respectively. The coupling efficiency and its relation to misalignments are studied.
We propose a flexible 2D bit-parallel optical interconnect method for use in large-bandwidth inter-processor communications. We have studied various possible input/output coupling schemes, and have modeled power loss and resolution degradation mechanisms associated with the schemes. We have also performed experiments to investigate the power efficiency and imaging resolution characteristics of the interconnect schemes.
We propose a new method for implementing a large optoelectronic (O-E) crossbar interconnect switch , Based on an emerging vertical-cavity surface-emitting laser (VCSEL) technology, a passive angle-multiplexed beam steering architecture is proposed as a key component of the O-E crossbar. Various optical system parameters are evaluated. Since there is no optical fan-out power loss, the interconnect capacity of the proposed system is determined by the diffraction-limited receiver power cut-off and therefore interconnection of more than 1,000 nodes with a per node bandwidth of 1 GHz using today's technology is possible.
Long data stream convolution is required by practical signal processing applications. Various algorithms for digital computers offer satisfactory results if the long processing time and large memory space are tolerable. We describe an algorithm suitable to the optoelectronic implementation of the real-time convolution of long data streams (104 to 106 points). Based on the Chinese remainder theorem, an N-point 1-D data sequence (N = r1r2, where r1 and r2 are mutually prime) is permuted to form a r1 x r2 2-D array. The convolution of two N-point 1-D data sequences is then realized by the convolution of their corresponding 2-D arrays. Free space 2-D optical systems can offer the benefit of real-time processing. Due to the huge amount of the required interconnects, optical schemes rather than electronic schemes are preferred to perform the 1-D to 2-D data permutation. We propose to implement a high-speed optoelectronic convolver for handling the long data sequences by using a standard 2-D optical convolver sandwiched between two optoelectronic data permutation devices. A modified cathode ray tube (CRT) and a standard CRT combined with an optical geometric transformer are described as examples of such devices. Various optical implementations of the convolution operation are also described and compared for this application. The entire algorithm was computer simulated for its optical implementation. Other practical problems and the fundamental limits are also discussed.
We revisit some fundamental laws of physics governing the light propagation in linear media in order to have a better understanding of the roles of optics for parallel interconnection of digital processors. The degree-of-freedom obtainable using optical techniques can be derived from the domains of space, spatial frequency, time, temporal frequency. We pinpoint various fundamental barriers and practical limits of optics for handling interconnections. Various schemes of using optical techniques to maximize the information transmission capacity while minimizing the channel complexity are also discussed.
In this paper, the design and implementation of a high speed optical ring topology based free space optical interconnect is described. This interconnect system operates at 500 MHz and consists of 16 laser transmitters, a four channel free space interconnect, and a fast speed receiver. A Nearest Neighbor interconnect has been successfully demonstrated. At the data rate of 500 MHz, the total system throughput is 8 Gbps. The system can easily be operated at much higher data rates since the rate was only limited by the electronic circuitry. A discussion is given about device issues such as optical switching devices and practical system design issues such as integration and interface with current electronic systems is considered. This interconnect is very promising in the implementation of ultra fast massively parallel SIMD machines.
Using what is available to free-space optics, it is possible to construct a 4D network which multiplexes the time, temporal frequency, space and spatial frequency channels so that the switching complexity is reduced from the order of N2 to the order of N5/4. We proposed and experimentally demonstrated a simplified version of this network based on some multichannel acousto-optic deflector arrays.
In this talk, based on the key operations governing all these matrix-matrix multipliers, we propose a statistical model to quantitatively analyze the numerical accuracy that these multipliers could deliver. Our study indicates that no matter what particular scheme is used, statistically the numerical accuracy limit caused by the use of analog computation mechanism is much more serious than the dynamic range and other limits to a matrix-matrix multiplier. Our study also shows that when these multipliers are used for, instead of generating algebraic results, the single threshold operations, such as the operations required to implement a programmable logic array, a content- addressable memory, and a neural network, a better accuracy can be expected depending on the used threshold positions.
Recent research indicates that while maintaining a basic mesh-type node layout, which has many proven practical advantages, an increase (from degree-4) in node connectivity can lead to various new and interesting networking properties. In this paper, we discuss possible optical methods to implement such a class of connectivity-enhanced mesh-based interconnect networks. Multiplexing capability that only free-space optics could efficiently offer is utilized in these methods. As particular examples, two interconnect schemes, one for a nonblocking broadcast switching, are described. While the first model, which aims to reduce he overall network diameter using extended node connectivity, offers a compact and scalable geometry and a fast routing capability, the second model, which aims to lower the switching complexity bound for nonblocking multicast interconnect applications, is extendable to multidimensional multiplexing. Advantages of using the free-space optics for implementing the two models are discussed. Some proof-of-principle experimental results are presented.
We discuss the potential of using free-space optical methods to implement a class of connectivity-enhanced mesh-based networks. As shown, the unique advantages that the free-space optics can offer, including large power fan-out per node capability, and the ability for spatial-angular multiplexing make it possible for connectivity-enhanced mesh-based networks to be efficiently implemented. In our presentation, two switching models, one for nonblocking point-to-point switching and the other for nonblocking broadcast switching, are described for their optical implementations. Some proof-of-principle experimental results are presented.
Recent advances in mathematical theory related to the representation of signals and images by some limited-extent-wave functions have generated substantial interest in applications of waveforms that are localized in both time (space) and frequency (spatial frequency) domains to signal and image processing, pattern recognition, data compression, and neural networks. As a particularly useful model, the so-called wavelet transforms provide a variety of multiresolution signal (image) time-frequency or space-frequency decomposition tools. Digital parallel implementations of the wavelet transforms are computationally intensive both because of the nature of the coordinate dilation and erosion of these transforms and because of the large quantity of convolution/correlation operations accompanied. This paper is intended to outline some of the most useful properties of the wavelet transforms, their similarities, and differences to other known joint representations. The links between the wavelet transforms and optics also are discussed.
A novel optical free-space mesh-connected bus (MCB) interconnect network architecture is proposed. An MCB is known to have the capability of interconnecting, using a three-stage switching, N nodes with a power distribution loss proportional to (root)N, and is therefore advantageous for networking a large number, say over 1000, of communicating ports. Based on conventional space-invariant optical components in a compact and efficient geometry, the proposed optical MCB system concept can be used to build either free-space optical interconnect links for parallel processing applications or central switching systems for local or global lightwave communication networks. The proposed architecture lends itself for networking under both the wavelength-division multiple-access (WDMA) and other multiple- access environments. In this paper, based on the WDMA environment, various optical system implementation and performance issues are discussed and parameters are analyzed. It was found that using a reasonably compact three-dimensional free-space volume, more than 100,000 dispersion-limited communication nodes at a uniform channel spacing of 0.75 nm can be linked with a moderate PDL of 28 dB. Some preliminary optical WDMA MCB experiments based on a 27 X 27 panchromatic optical source array were performed to confirm the operational principle of the proposed concept.
1-D scan that follows the Peano curve to a desired resolution is demonstrated to preserve a 2-D proximity relationship and is shown to be efficient for wavelet transform (WT) processing and artificial neural network pattern recognition. This deterministic fractal sampling method can be implemented in real time using optoelectronic scanning. For example, 2-D texture patterns are analyzed by using 1 -D wavelet transformation. Those WT coefficients can be fed into a standard back-propagation neural network for pattern recognition.
Recent development in vision and image understanding related study reveals that a signal decomposition before processing may provide an enormous amount of useful information aboutthe signal. Various signal decomposition models such as the Gabor and wavelet expansions have been proposed. While the Gabor signal expansion creates a fixed resolution space-frequency signal representation, the wavelet transform provides a multiresolution signal space-scale decomposition. Digital implementation of these expansions are computationally intensive both because of the nature of the coordinate-doubling of the transforms and because ofthe large quantity of convolution/correlation operations to be performed. Optics with its inherent parallel-processing capability has been applied to many useful linear signal and image transformations for feature analysis and extraction. We studied the suitability of using optical processing techniques for the signal Gabor and wavelet analysis. Gabor and wavelet expansions of both 1- and 2-D signals and images are discussed. System parameters and limitations are analyzed. Preliminary experimental results are presented.
Convolution of long sequences of data is often needed for various sensing, signal processing, and pattern recognition applications. In this paper, massively parallel opto-electronic interconnect schemes are proposed to solve the problem of real-time convolution of long (104 - 106) data systems. Based on the Chinese remainder theorem, a 1D data sequence of length N (N equals r1r2, where r1 and r2 are mutually prime to each other) may be permuted into a 2D array of a size r1 by r2. A convolution of the two 1D data sequences each of N points is therefore converted into a convolution of the two corresponding 2D arrays each of a size r1 X r2. A standard 2D optical image convolver sandwiched between an input and an output opto-electronic data permutation devices (interconnect networks) can thus perform the required convolution. Two video rate opto- electronic data permutation schemes which are based on: (1) the use of a modified cathode ray tube (CRT) and (2) a combination of a standard CRT and an optical geometric transformer, respectively, are described. The permuted 2D data are subject to a standard free-space optical convolution before a 2D to 1D inverse permutation to generate the final 1D convolution result. Computer simulation for the entire three-stage algorithm and their results are discussed. Technical problems and fundamental limitations of the proposed schemes are also discussed.
We consider two new techniques (wavelets and Gabor transforms) plus morphological methods for use in the detection, image enhancement, and feature extraction stages of scene analysis. We find the new wavelet and Gabor methods to be of potential use for textural/statistical measures that complement other established methods. The optical realization of all methods on a unified optical correlator architecture is noted. The dimensionality problems of the two new methods should be solved by use of linear combination filters (LCFs) of several wavelet or Gabor functions.
As an extension of an existing electron beam deflector, an optical analog-to-digital (A/D) conversion scheme is presented. As a fast theta modulator, a wide-band acousto-optic (A-O) deflector that performs a voltage to optical beam deflection angle mapping is used. Using a GaP A-O deflector, a proof-of-principle 6-bit A/D converter is experimentally demonstrated.
An optically implementable algorithm, which separates a long data stream into several shorter sequences based on the Chinese Remainder Theorem (CRT), is described in this paper. Using this algorithm, the convolution/correlation of long data streams are performed by small scale vector-matrix multiplications, which can be realized using the state-of-the-art optical algebraic processing technologies. Computer simulation results of this algorithm are presented. A suitable optical processing architecture is also proposed.
An opto-electronic Gabor detector for transient signals is proposed. Using an acousto-optic modulator as its input device, a liquid crystal SLM as a reconfigurable window and a two dimensional CCD detector array, a real-time opto-electronic detection architecture based on the Gabor representation of signal is described. Some preliminary experimental results are presented.
A new optical Fourier domain filtering scheme that combines the conventional optical
space-invariant linear filtering with a self-pumped nonlinear optical phase-conjugation
technique is proposed. The new method is used for a real-time detection and channel
evaluation of the multi-path information needed in radar, sonar, and communication signal
processing applications. Preliminary experimental demonstrations are included.
A new scheme for digital optical computing, utilizing a non-holographic opto-electronic addressable memory (CAM), is discussed. To illustrate the performance of this arithmetic processor, the design of an optical binary carry look-ahead adder (CLA), also, the design of a binary, a logarithmic number (LN) and a residue number (RN) multipliers are presented. Compared to existing opto-electronic approaches, this non-holographic CAM offers a number of practical advantages, such as fast processing speed, ease of optical implementation and alignment. Two spatial input data encoding techniques, an active low and high, are discussed. A multioperation multibit CAM processor is presented. Experimental results for a CLA adders; and a binary, residue and logarithmic number multipliers are also presented.
Several new higher-order spatial symbol recognition methods for optical symbolic
substitution-based calculations are presented. In case of logic processing, higher-order
symbolic substitution (SS) rules can be applied to implement multi-variable logic functions.
In binary arithmetical calculations requiring carry propagation, the simultaneous processing
of a number of bits increases computational speed. Finally, using higher-order SS rules,
image processing can be perform using larger windows. Both, multiplicative and additive
techniques for a spatial symbol recognition are discussed. Four different optical architectures,
a multi-reflecting technique using an optical cavity, a correlation, a phase conjugation
and a content-addressable memory (CAM) techniques, are suggested. Optical either
dual-rail (DR) or triple-rail (TR) spatial encoding is employed. Some preliminary
experimental results are also included.
The modified signed-digit (MSD) number system, because of its inherent weak interdigit dependance, has been suggested as a useful means for a fast and parallel digital arithmetic. To maintain a fast processing speed, a single-stage holographic optical content-addressable memory (CAM) based MSD algorithm was suggested. In this paper, a novel non-holographic opto-electronic CAM based fast MSD addition processing architecture is proposed. The proposed concept has been verified with our first-order proof-of-principle experiments. A figure of merit comparison of this and other existing approaches is also presented. Based on this key opto-electronic CAM element, implementation of more sophisticated I'VISD arithmetic, such as optical MSD subtraction and multiplication operations, are proposed.