An optical computing method for string data matching applicable to genome information processing is presented. With encoding 1D data into spatial code patterns, moire fringes between two different coded patterns provide information on the correspondence of the original data, which is useful for string alignment in genome analysis. A new code set for the spatial coding is capable of processing complementary base-pairing DNA sequences. Results of the preliminary experiments are shown to verify effectiveness of the method. Processing performance is evaluated with a simplified model. Finally, two optoelectronic implementations are presented for future directions.

We present a novel and simple theoretical model of computation that captures what we believe are the most important characteristics of an optical Fourier transform processor. We use this abstract model to reason about the computational properties of the physical systems it describes. We define a grammar for our model's instruction language, and use it to write algorithms for well-known filtering and correlation techniques. We also suggest suitable computational complexity measures that could be used to analyze any coherent optical information processing technique, described with the language, for efficiency. Our choice of instruction language allows us to argue that algorithms describable with this model should have optical implementations that do not require a digital electronic computer to act as a master unit. Through simulation of a well known model of computation from computer theory we investigate the general-purpose capabilities of analog optical processors.

Digital simulations have previously shown that automatic recognition of out of plane rotated and scaled objects can be performed by wedge compression of the power spectrum and feature space trajectory algorithms. We implemented this recognition system optically. We used an opto-electro- mechanic angular sampling of the power spectrum to perform the feature extraction. Preliminary results using this system are presented.

In this paper, we report for the first time the feasibility of coding by coherence modulation in 2D optical correlator using a spatially and temporally incoherent light source. This technique allows to carry out simultaneously several correlation products. The reported results have been obtained with a broadband source, such as a white-light source.

A different image encoded by polarization coding generates a different polarization distributed on its Fourier plane. This fact enables to realize pattern detection with polarization. The method is reported better capability to discriminate gray-level images. It has been formerly reported that we have implemented the polarization coding and polarization spatial filter using liquid crystal spatial light modulators with phase modulation and optical rotatory power. In recent years the use of bacteriorhodopsin (BR) as a holographic recording material has been studied intensively. BR films are sensitive to polarization because the BR is the photoinduced anisotropic material. In this paper, we propose the possibility of bacteriorhodopsin films for polarization spatial filter and investigate simplification of pattern detection system with polarization information.

The performance of a novel acylate-based thermally stable photo-polymer is presented. Rapid direct writing of the guides and other structures is realized using a high-power 325 nm He:Cd laser. The loss is measured by cut-back to be less than 0.17 dB/cm at 850 nm and less than 0.5 dB/cm at 1310 nm. This material and writing system is used to make 50 micrometers square core cladded guides and compliant bumps for device attachment, and 45 degree(s) TIR mirrors for out of plane coupling.

In this paper an optical interconnection technology for high-speed printed circuit board application is presented. This technology is widely compatible with the existing design and manufacturing technologies of conventional multi- layer pc boards and it combines electrical and optical interconnects on pc board level. Using this interconnection technology on-board bandwidth of several Gbps can be realized. As conventional pc board technology provides sufficient performance characteristics for the majority of all on-board signals only a hybrid technology which is compatible to the existing printed circuit board design and manufacturing processes is able to lead to a practical solution at reasonable cost. This compatibility demand results in different technological, functional, and economic requirements which also consider potential application for high performance computing and telecommunication hardware. In this paper an overview is given on the requirements, on the basic technologies for manufacturing electrical-optical pc boards as well as on the extended design process with its modeling and simulation methodologies and strategies.

Optical links are expected to overcome the limitations imposed by electrical links even for short transmission distances as they have done in telecommunications trunk networks. For board-to-board and board-to-multiboard communication we have developed an optical backplane for applications in mobile systems. Compared to fiber based realizations it is compact, rugged and has the potential to be fabricated at low cost. The main features of the optical backplane in planar technology are free space expanded beam transmission between boards and backplane and guided wave transmission within the backplane. No optical connectors are required. Due to the expanded beams and highly multimode waveguides large coupling tolerances of several 100 micrometers are achieved. Low loss polymer backplane waveguides (3 dB/m) allow transmission lengths of more than 19'. Demonstrators for board-to-board interconnections and star networks have been realized. Transmission experiments at 1 GBit/s have been successfully performed. Environmental tests prove the thermal stability of the polymer waveguides.

In this paper, we present a new packaging architecture for chip-level optical interconnections based on imaging fiber bundles. Imaging fiber bundles consist of densely packed arrays of small core fibers such that an object imaged at one end of the bundle is correspondingly imaged on the opposite end. In optical communication applications fiber bundles can be directly coupled to an array of optical sources. Each spot is carried by multiple fibers that in turn can directly illuminate each element in a detector array. Neither end requires any additional optical elements. Thus, imaging fiber bundles are capable of supporting the spatial parallelism of free space interconnects with relaxed alignment and geometry constraints. This paper is focused specifically on multi-chip system designs.

Angle division multiplexing (ADM) is a multiplexing scheme which is applicable to optical signal transmission through multimode step-index fibers. ADM allows for parallel and high-bandwidth transmission by using passive components, i.e. no external control is necessary. The fiber quality limits the simultaneous optimization of transmission distance, number of channels and cross-talk. This paper reports on first experiments with an ADM based data link over 10 m between workstations with 8 Gigabit-Ethernet channels at a cross-talk of better than -10 dB. For a micro-optical integration of the ADM system design rules and tolerance considerations are discussed.

Objects that temporally vary slowly, may be super resolved using two moving masks such as pinhole or grating. The setup requires two physical gratings that should move in a synchronized manner. This approach is efficient for exceeding the resolving capability of Abbe's limit. Moreover, it was based on coherent illumination and required a certain approximation. In this work the second grating, which is responsible for the information decoding, is replaced by a detector array and post-processing procedures. This way, the synchronization problem existing when two gratings are used is simplified. Furthermore, two novel approaches for getting accurate coherent super-resolution and overcoming the distortions exhibited by Ronchi gratings and manufacturing imperfections are also presented. In the first approach the grating in the image plane is moved with a velocity which is half the required velocity. In the second approach, different parts of the spectrum are transmitted through the system's aperture that allows a post processing ability. Experimental results are provided for demonstrating the ability of the new approach.

Optical computing is applicable to very large database problems that require several iterations of processing. One such forthcoming problem is the analysis of DNA data, in which an individual in a population may have billions of bases in their DNA structure. Current methods only find simple first order associations between the DNA structure and the expressed illnesses. This means that the presence or absence of a gene strongly influences the onset of an illness. These current methods will have a difficult time in finding higher order associations between the genome and the expressed phenotypes. The discovery of such associations will take several iterations through a large database to extract association information. Searching a database of billions of elements for each of hundreds of individuals through thousands of iterations is prohibitively expensive on electronic concepts. Highly parallel architectures such as optical correlators will offer the opportunity to process this large amount of data in a higher-order fashion.

We propose a new approach for the 2D space-to-time conversion which can directly ultrafast convert an input 2D spatial signal into a modulated ultra-fast temporal optical pulse sequence. It is aim at developing a new technique for ultra-fast conversion between image signals and time sequential ones. The proposed technique consists of combined uses of the concepts of time-space conversion, the time- frequency transform, and their inverses.

In holographic data storage, pages of information are overlapped in the volume of the recording medium. Due to destructive read-out of holograms in photorefractive crystals such as LiNbO₃:Fe, holograms are recorded with an exposure schedule in order to equalize diffraction efficiency. This leads to a final diffraction efficiency proportional to 1/M², where M is the number of exposures. Coherent erasure of a particular page also erases all the other pages stored in the same volume. We believe to have found a technique that does not require an exposure schedule and that can record M holograms with diffraction efficiency following a 1/M dependence. Our technique is based on non-destructive read-out in doubly-doped LiNbO₃. The technique is based on the recording of localized holograms in thin layers across the volume of the crystal.

Two-photon 3D optical data storage techniques can achieve hundreds of GB data capacity per disk by storing data in multi-layer volumetric media. This approach can also provide fast data transfer rates by using parallel access techniques. It is a promising solution for the high data capacity demands in imaging and video applications, and the high-speed data access requirements in large-scale high- speed data processing. Development of this technology integrates and leverages developments in parallel sensors, spatial light modulators, novel optics, parallel signal processing, and micro-optic packaging.

Volume holographic memories (VHM) achieve large storage capacities by multiplexing many holographic data pages in a small volume. On retrieval, a reference beam addresses the optical memory reconstructing the desired hologram with a large diffraction efficiency. In addition, all the other multiplexed holograms also reconstruct at a very low diffraction efficiency as determined by the Bragg selectivity function (BSF) of the VHM. To achieve low crosstalk the multiplexing scheme stores pages on the periodic nulls of the BSF. Absorption in the crystal corrupts the nulls requiring an increased multiplexing spacing between pages. Analysis of grating formation in photorefractive crystals relates the BSF to the transverse spatial electric field of the reference beam. This permits apodization of the reference beam as a method to shape the Bragg selectivity function and hence control the crosstalk noise. Furthermore, apodization can be incorporated into the VHM system metric, M/#, by considering the adjusted recording slope and reconstruction illumination. Theoretical predictions show that apodization can strongly attenuate the crosstalk noise allowing high multiplexing density in exchange for a small loss in the system M/#.

We demonstrate a method of obtaining scale invariance detection using a white light optical correlator. We are able to detect different scaled versions of the target in the same scene up to a magnification factor equal to 2. Each scale factor is codified in a different wavelength so each scaled version of the target is detected with a correlation peak of different wavelength. Experimental results demonstrate the proposed technique and show the utility of the method here introduced.

A hybrid opto-electronic correlator for detecting defects in optical fibers is proposed. After the light from a He-Ne laser being expanded and filtered, it is not collimated but directly passes a Fourier transform lens and illuminates a fiber to be detected and a perfect fiber as reference one at the input plane. The Fourier transform spectrum of the fiber pair is obtained at the rear focal plane of the lens, where it is sampled via a CCD array connected with a computer through a frame grabber. The computer performs filter, inverse Fourier transform and setting threshold operation on classification. Under specific conditions, the system is an equivalent of joint transform correlator with a Fourier lens of long focal length. We analyze the conditions in terms of theory and show the experiment results corresponding to optical fibers having incoordinate defects. The results indicate that the system can be used for fiber defects detection, and it has the advantages of high identification, compact configuration, easy adjustment and flexible manipulation.

Fraunhofer diffraction at finite distances can be produced by a variety of optical setups. Convergent arrangements, in which the diffracting object is illuminated by a converging spherical wave-front, are of special interest since they enable an easy control over the size of the resulting diffraction pattern. In particular, such arrangements are frequently used in optical correlators as a means to obtain the Fourier transform in the input scene. We analyze the effect of the wave aberration introduced by the convergent optical system in the resulting Fourier transform, both experimentally and by a computer simulation, as well as its impact over the correlation plane. Also, we introduce a simple optimization method that gives good results in alleviating the loss of space invariance, which is the most important side effect found in the study.

This work presents a 3D scanner system based on stereovision techniques to generate plane views of an object from an arbitrary viewpoint. These views are used as the reference templates in an optical correlator system designed to recognize the object.

We present approaches for visible and infrared video image sequence registration, useful for image fusion, target detection and recognition. For the visible and mid-infrared images of well-separated spectral bands the challenge in image registration is the feature inconsistency and low contract and noise in the infrared image background. Possibility of integrating the optical correlator into the operational systems is discussed.

We characterize the bounds on numerical accuracy that a finite acoustic beam height will have on an analog acousto- optic algebra processor that uses coherent illumination. A Fourier optical model of our physical matrix-vector multiplier is used as a basis for the simulations.

The optical implementation of neural networks using volume holograms for weighted interconnections requires stable phase relation between input channels. This is particularly important for images with variable illumination. One way to solve this problem is to use binary inputs. The simplest binarization is the direct quantization, but this method has a number of disadvantages. Error diffusion algorithm is more robust under variable illumination since it keeps the original image characteristics.

The principles underlying optical correlators and Fourier transform optical memories are well understood. The components and materials they depend upon are gradually becoming available, bringing these technologies closer to commercialization. As efforts are made to obtain the best possible performance from these systems it becomes increasingly important to understand how their detailed operation differs from simple idealized models. Spatial light modulators (SLMs) used in correlators display sets of discrete data rather than continuous 2D functions, and the optical Fourier transform of these SLMs is influenced by the shape and fill-factor of the SLM's pixels. As a consequence, optical correlators perform a function that is more complex than the simple idealized correlation operation. The performance of Fourier transform optical memories is similarly affected. Here we investigate the operation of such optical systems incorporating pixelated SLMs. Examples are presented which highlight differences between the functions actually performed by these systems and the simple conceptual models of their operation. The output of these systems is commonly detected using pixelated CCD or CMOS imagers, the effect of imager pixel fill-factor is also examined.

We performed detailed characterizations of the transient nematic effect in parallel aligned nematic liquid crystal cells and adapted this technique to blazed phase gratings operating in the 1.55 micrometers telecommunication window. With reflective cells, on/off response times lower than 50 and 2 ms, respectively, have been observed with an appropriate design of the voltage sequences applied to the different electrodes.

Experimental investigations of generations and processing of optical patterns in a nonlinear optoelectronic circuits composed of an electronically addressed spatial light modulator and a CCD camera are described. The circuits generates rolls and hexagons, whose pitch has the square root dependence of the spatial frequency upon the positive and negative diffraction length. In compared with a nonlinear optical circuits composed of optically addressed spatial light modulator, the nonlinear optoelectronic circuits have the wide range control of nonlinearity and temporal property, less constraints in an optical and electrical mappings, and a low light level derived from high sensitivity of the CCD camera. We also demonstrate the synchronization of the generated patterns using the optoelectronic circuits with the electronically simulated point nonlinearity and nonlinear mapping.

Image processing in general and optical image processing in particular require very accurate and very complex processors. Such processors are sometimes difficult to manufacture and expensive to purchase. They also might be non flexible in their design. The principle of generating a single processor by use of several simpler processor-modules in cascade (and/or in parallel) is quite familiar. However, in optics this approach is mainly used for filtering in the Fourier or fractional Fourier planes. In this work the authors introduce multi-stage optical processing in the Fresnel plane. Using a small number of binary masks (either amplitude or phase) along the path of the light, one may process the incoming beam in the same manner as using a single high-resolution complex mask. The authors present an algorithm for establishing the binary processors and introduce the results obtained by this approach. An important application of this technique is the field of image recognition. Simulations demonstrate that minor manipulations on the input, affect the output plane significantly. On the other hand, hiding fractions of the input pattern hardly influence the output whereas the obtained effect reveals information regarding the flaw inserted within the input pattern.

In this paper, we investigate the imaging properties of curved large diameter (approximately mm) Gradient Index Polymer Optical Fiber (GIPOF) for massively parallel optical interconnects. We consider that in such large fiber light can propagate following the law of geometrical optics. A program of ray-tracing through curved GIPOF has been developed based on an algorithm proposed by Sharma et al. From simulations we found out that some S-shaped fiber patterns can fulfill at the requirements needed for flexible parallel board-to-board optical interconnects, namely small spot size, low distortion and high transmission efficiency if small divergence angle sources such as VCSELs are used. However the shape and the length of the fiber should be well controlled and the displacement between optoelectronic chips should not exceed a few centimeters.

We propose an application specific optoelectronic parallel computing architecture as a solution of the optical computing system to demonstrate the usefulness of optics in information processing system of near future. Solving optimization problems based on the genetic algorithm is studied as a target of the proposed architecture. The composition of the proposed architecture is described. Validity of the operation of the proposed architecture is verified by computer simulation. Processing performance of the system based on the architecture is analyzed and its advantageous conditions comparing with the electronic multiprocessor system are clarified. An optical image broadcaster is constructed to demonstrate the capability of optics in the system and the experimental results are presented.

We investigate some limiting characteristics of two- component optoelectronic system for information transmission on the base of number-state model and Brillouin's negentropy principle. The expression for the upper bound of the capacity of considered communication system is obtained. It is shown, that the capacity of the whole system is substantially limited by the speed characteristics of an optical subsystem. Only in the limited power range of optical signal it is determined by speed of the information transmission in an electronic subsystem. Such a consideration enables us to get deeper insight into the basic principles of information processing in channels with different nature of carriers.

One of the main challenges involved with the successful implementation of free-space optical interconnections is associated with the issue of misalignment. Small misalignments of the components can substantially decrease the coupling efficiency between the source and detector. The alignment problem can be tackled in various ways: the most straightforward solution consists in designing the system to be as misalignment tolerant as possible by using slow f- number beams, oversized apertures or a beam clustering design. Having chosen a suitable design it is then necessary to implement it in such a way that the possible misalignments of each component are minimized, while requiring minimal active alignment control. This paper reports on the implementation of a dense 256-channel free- space multistage optical system which interconnects 4 optoelectronic VLSI chips in a square baseplate 7 cm on a side. Alignment strategies, constraints and experimental results are presented.

A folded structured light generator is presented. This spot array generator is to be used in a modulator-based free- space optical interconnect. Three cascaded diffractive optical elements produce 4 X 8 clusters on an 800 micrometers X 1600 micrometers pitch, where each cluster is a 4 X 4 array of 13.1-micrometers -radius spot on a 90-micrometers pitch. The folded configuration is more compact than an existing linear spot array generator. Details of the optical design and assembly issues are presented.

An optical circuit was designed and built to facilitate the testing of a free-space optical interconnect. Details of the optical design are presented. The interconnect was based on a hybrid CMOS/GaAs chip which had a 16 X 16 array of detectors on a 250 micrometers pitch interlaced with a 16 X 16 array of modulators. The optomechanics enabled two such chips, bonded to printed circuit boards, to be mounted, positioned and aligned relative to each other. The operating wavelength of the devices was 827 nm. The optical system worked successfully and alignment could be achieved across the array with ease and high precision.

An intelligent interconnection network with fine-grain parallelism is described that has the potential to support efficient, scalable algorithms running on associated coarse- grain processors. The approach is relevant to the emerging computational cluster systems. The support of concurrent operations within the network is discussed and their mapping onto smart-pixel array network interfaces is shown. Choices are considered in the design of the free-space optical interconnect that enables the inter-smart-pixel-array communication. In particular, a system that uses multi- element macro-lenses is studied and results of detailed modeling are given that quantify the smart-pixel density. These results are used, in an illustrative case study of the sorting problem, to compare potential system architectures. This is work in progress and throughout the paper, important issues in the design and use of the intelligent interconnect are raised that require more study.

We propose an optoelectronic parallel-matching architecture (PMA) that provides powerful processing capability for distributed algorithms comparing with traditional parallel computing architectures. The PMA is composed of a parallel- matching (PM) module and multiple processing elements (PE's). The PM module is implemented by a large-fan-out free-space optical interconnection and a parallel-matching smart-pixel array (PM-SPA). In the proposed architecture, each PE can monitor the other PE's by utilizing several kinds of global processing by the PM module. The PE's can execute concurrent data matching among the others as well as inter-processor communication. Based on the state-of-the-art optoelectronic devices and a diffractive optical element, a prototype of the PM module is constructed. The prototype is assumed to be used in a multiple processor system composed of 4 X 4 processing elements, which are completely connected via 1-bit optical communication channels. On the prototype demonstrator, the fundamental operations of the PM module such as parallel-matching operations and inter- processor communication were verified at 15 MHz.

Planar and spatial lightwave (LW) switches (synonym: all- optical switches) are reviewed and compared with regard to their (1) architectural principles (2) possible implementations and (3) performance. The first step towards spatial LW switches are spatial LW coupler which are aimed to utilize symmetries and circular geometries covering several planar LW couplers. Then spatial LW switches, capable to generate simultaneously several rearrangeable nonblocking interconnections, are the next more involved step. The goal are switch architectures with a low number of subsequent switching sections/stages. The spatial LW switches may be applied as (1) single components and (2) switches within large 3D LW circuits. For integrated switch architectures principle problems arise and the restriction of the number of layers causes additional difficulties.

A 2 X 2 optical switch performing bidirectional cross-bar on optical communication signals at 1550 nm is presented and experimented. The switch is based on electro-optic effect in bulk CdTe crystals. Operation is totally independent by input state of polarization of the optical beams to be addressed. The proposed free-space architecture grants high compactness, reliability and fast response time compared with common switching solutions.

We present the design and the system characterization of a 8 X 8 free-space optical switching matrix based on the cascade on two 1D deflectors. These devices are based on phase ramps generated into parallel aligned nematic liquid crystal cells. Each cell is divided into 8 arrays with 309 2.5 micrometers -wide electrodes. Each of these arrays is addressed by Tape Automatic Bounded circuits which are reported onto the transparent Indium Tin Oxide on glass substrate. A specific software allows to determine the supply voltages required to establish a given set of interconnections. The two liquid crystal cells, which have been optimized to operate in the 1.55 micrometers window, have an efficiency higher than 70% for deflection angles up to 2.5 degree(s). These cells have been associated with single mode fiber and diffractive lens arrays into a rack-mounted demonstrator, which include the required optics to achieve polarization diversity. The average insertion loss is 9.0 dB with a maximum of 12.5 dB; the polarization dependent loss is lower than 1 dB, and worst case isolation is about 30 dB.

New optoelectronic interconnect hardware such as FCPT's Scalable System Film Component and Film Optical Link Module, and an increase in the number of optical devices in interconnect systems are raising the following desires; `3D optical wiring in a free space' and `self-aligned optical coupling'. Self-Organizing Lightwave Network (SOLNET) may provide the solution. SOLNET utilizes attractive force generated between light beams in photo-refractive materials, enabling straight/downtapered waveguide construction in a free space and automatic waveguide formation between optical devices. Proof-of-concept of SOLNET is demonstrated by computer simulations and experiments.

A novel approach to photonic A/D conversion using a distributed neural network, oversampling techniques, and a smart pixel hardware implementation is described. In this approach, the input signal is first sampled at a rate higher than that required by the Nyquist criterion and then presented spatially as the input to a 2D error diffusion neural network consisting of M X N neurons, each representing a pixel in the image space. The neural network processes the input oversampled analog image and produces an M X N pixel binary or halftoned output image. Decimation and low-pass filtering techniques, common to classical 1D oversampling A/D converters, digitally sum and average the M X N pixel output binary image using high-speed digital electric circuitry. By employing a 2D smart pixel neural approach to oversampling A/D conversion, each pixel constitutes a simple oversampling modulator thereby producing a distributed A/D architecture. Spectral noise shaping across the array diffuses quantization error thereby improving overall signal-to-noise ratio performance. Here, each quantizer within the network is embedded in a fully- connected, distributed mesh feedback loop which spectrally shapes the overall quantization noise thereby significantly reducing the effects of components mismatch typically associated with parallel or channelized A/D approaches. This 2D neural approach provides higher aggregate bit rates which can extend the useful bandwidth of photonic-based, oversampling A/D converters.

In this paper, we analyze the steady state and the temporal response of cross-polarized four-wave mixing and show that it is possible to stabilize the gain of optical bus line with the PRCM (Photorefractive Connection Module). We analyze the temporal response of the signal intensity and find the optimum setting for the signal and control beam intensities. We experiment on the two stage optical bus system and evaluate the stability of the bus line.

We discuss the design of a compact parallel joint transform correlator (PJTC) using four binary zone plate array as a Fourier transform lens. The external dimensions of the hybrid opto-electronic correlator is 23 cm X 15 cm X 16.3 cm, which includes the PJTC system in the upper stage and some of driving circuits and an LD for a light source in the lower stage. Experimentally, we implemented this compact PJTC system for facial recognition with database of 100 persons and obtained reliable discrimination results. Furthermore, we propose a novel method of pre-processing so that any general users could easily operate the compact PJTC system and constantly obtained the same size extracted images, by fixing three points; the edges of both eyes and the low end of nose, when normalizing the facial image size. We confirmed the ability of our system to meet the conditions for recognition by JTC.

A fully complex filter is discussed using a Boulder Nonlinear Systems Smectic A* liquid crystal spatial light modulator. Each pixel is capable of both analogue amplitude modulation and binary phase modulation. Two pixels are used together in a macro pixel giving full complex modulation.

Optical correlators have been the subject of a growing interest over the past few years, since they enable a very fast computation of correlations, which are a major step in the design of many image processing algorithms. In this articles we will focus on the use of the nonlinear joint- transform correlator used as a location algorithm, which has been shown to provide good performances in terms of discrimination ability, and probability of correct location. When a optical correlator is used, the question of the choice of a method for encoding the input images arises. By the use of numerical simulations, we show that if the object to be located is perturbed by nonoverlapping noise, phase encoding can improve the correlation performance compared to amplitude encoding. We have recently provided a phenomenological interpretation of this fact, based on the histogram modifications undergone within the target and the background. We analyze here more precisely these modifications and extend these results to some realistic situations when the only knowledge about the target is its shape.

The departure between a reference range image and an acquired one is assessed using correlation. Decision criteria have been defined. Performance of coding and filtering are discussed. Results obtained on a Vander Lugt correlator with two twisted nematic spatial light modulators are given.

We propose a new approach for the 3D correlation. We compute directly the correlation integral without using the Fourier transform in the third dimension where the space bandwidth product of the sampled signal is small. We reformulate the 3D Fourier transform with a surface object model and the Lambert's Law. We discuss the means for recovering the object surface relief height function.

In this work we propose a method to obtain single centered correlations with an optical setup based on a joint transform correlator. This approach is a modification of a previous procedure that required displaying devices with a full 2(pi) phase modulation. The displaying requirements are less restrictive than before, allowing the use of many modulators and configurations. This new method is based on a binary power spectrum and it needs an interferometric process to obtain a single detection peak. To validate our new procedure, we propose an optical setup and we present the experimental results achieved.

Two methods for intensity invariant pattern recognition based on the summation of correlations between multiple binarized orthogonal gray scale images are proposed. The sliced orthogonal nonlinear generalized correlation uses the internal gray scale informations of objects. If the level of illumination of an object changes, the internal gray scale information of the object itself is preserved, although it is shifted. The first method is based on the normalization of segmented targets, and the second deals with the whole input image without segmentation and without normalization. Computer experiments show that correlation peaks of equal intensity are obtained for true objects with different unequal illuminations, and that the methods are very good at rejecting false targets in the presence of correlated disjoint noise. Because the second method is based on multiple linear correlations, it can be implemented optically with a joint transform correlator.

A multi-layered optoelectronic parallel processing system, which is called Optoelectronic Computer Using Laser Arrays with Reconfiguration is shown. This system consists of layers of processing modules, which are composed of electronic programmable processing element array each having parallel optical input/output connected by optical interconnection modules. Every module is designed to be modular and cascadable. The algorithms for this system are also shown which exploit the aggregate bandwidth supplied by optics and the computation versatility given by electronic processors.

We describe the design and implementation of a free-space optical interconnect for multi-processor and backplane applications. The system is designed to interconnect 4 nodes in a unidirectional ring, with a total of 256 data channels propagating from node to node. Each node contains an array 512 GaAs electro-absorption modulators and 512 photodetectors, hybridly attached to a silicon integrated circuit. Light is relayed between nodes with a rigid micro- optical system. System results are presented.

The physical limit on electronic data communication rates between silicon chips is projected to be of the order of Tbit/s over cm-scale connections. The semiconductor industry predicts that this level of i/o is likely to be required in the near future. Free-space optical connections to silicon VLSI are potentially able to offer much higher data-rates than electrical interconnects and are promising for future high-performance electronic systems. We have assembled the components of an optoelectronic 15 Gbit/s crossbar switch designed to include, internally, an optical data rate to a hybrid InGaAs/silicon chip in the Tbit/s regime. Input to the demonstrator is by an 8 X 8 VCSEL array operating at 250 Mbit/s channel, and these 64 channels are fanned out 8 X 8 times to give the high data rate onto the hybrid chip. This chip includes an array of 4096 InGaAs-based detectors flip chip bonded to silicon CMOS. The custom- designed CMOS performs packet routing under the control of an optical clock and the routed signals are output via differential modulator pairs, interlaced between the detectors on the InGaAs chip.

A novel board-to-board free space optical interconnect which operates on the principle of redundancy is described. Tolerance to misalignment is achieved through the use of 2D arrays of lasers and detectors together with an adaptive alignment algorithm based on redundant transceivers and a defocused optical interconnect. In this system, four 1.25 Gb/s data channels are supported by transmitter modules and receiver modules (2 per board) which contain 3 X 3 VCSEL and 3 X 3 photodiode arrays, respectively. The system was designed to have lateral misalignment tolerance of +/- 1 mm and angular tolerance of +/- 1 degree(s).

A novel device able to perform a real-time recognition of a temporal stream of optical bits at the communication wavelength of 1550 nm is presented. First experimentation with byte streams at 2.5 Gbit/s coming from a standard transmission line shows the capability of the device to produce the recognition optical signal in a PRBS continuous data flux.

Future data networks are required to support numerous high- capacity connections while providing simplified management and connectivity. To meet these requirements, we propose to utilize broadband ultrashort light pulses (ULP) in conjunction with pulse position modulation (PPM) as an efficient modulation format and code division multiple access (CDMA) for interference suppression. This networking format is operated asynchronously for simplified control, and requires minimal management for ensuring that the number of active users is below the limit at which multi-user interference generates excessive errors. The pulse positions can be detected at the receiver with high temporal resolution by utilizing a time-to-space conversion operating in real-time. The performance of the PPM/ULP-CDMA is found to depend on the following parameters: the ULP duration, the bandwidth of each spectral chip of the CDMA filter, and the ULP repetition time. We find that employing PPM improves the performance of the system relative to On-Off Keying. The performance can be further improved by increasing the number of PPM symbols, reducing the spectral chip bandwidth, and reducing the ratio of the pulse duration to repetition time. The performance analysis shows that the proposed system operates at a high bandwidth efficiency.

This paper proposes and demonstrates a novel type of a vision chip that utilizes pulse trains for image processing. The chip is based on a pulse frequency modulation (PFM) technique, which is used in neurobiological systems. Two types of chips are designed; one is a pixel TEG (test element group) chip for testing availability of PFM for image acquisition using 0.35 micrometers triple-metal double-poly CMOS process and the other is for a vision chip with inhibitory interconnections using 1.2 micrometers double-metal double-poly CMOS process. The TEG chip works well in the power supply voltage of 0.7 V and has a dynamic range of 20 dB with a power consumption of less than 1 (mu) W. The operation of the mutual inhibition in the vision chip is confirmed by simulation. Also the comparison with the other pulse modulation technique, pulse width modulation is discussed.

We report a means of fabricating hydrophilic domains in a hydrophobic background by lithographically patterning an adhesive hydrophobic layer. Organic polymer microlenses have been fabricated on these substrates using a dip-coating technique. Various lens shapes (circular, elliptical, square) have been fabricated on a variety of substrates (SiO₂, SiN, GaAs, InP, etc), ranging in size from 2 - 500 micrometers in diameter, and having fill factors of up to 90%. Plano-convex and double-convex lenses have been fabricated as fast as f/1.38 and f/1.2, respectively. The performance of arrays of these microlenses was quantitatively analyzed and optimized.

Innovative approaches to the packaging of a high-performance module accommodating a 32 X 32 array of surface-active devices indium bump bonded to a 9 X 9 mm² VLSI chip are described. The module integrates a mini-lens array, a copper heat spreader, a thermoelectric cooler and an aluminum heatsink. The mini-lens array is aligned and packaged with the chip using a novel six degrees of freedom alignment technique. The module is compact (44 X 44 X 45 mm³), easy to assemble and can be passively removed and inserted into a free-space optical system with no need for further adjustments. The chip is mounted directly on a flexible printed-circuit board using a chip-on-board approach, providing 207 bond pad connections to the chip. The junction-to-TEC thermal resistance is only 0.4 degree(s)C/W.

We present a packaged free-space optical interconnect, based on the Optical Transpose Interconnect System, which is designed to provide a bi-directional interconnection between two optoelectronic chips each of which contains thirty-two modulators and detectors. The optical system consists of two polarization-selective computer generated holograms, which combine a 4 X 8 lenslet array for illumination of the modulators and a 2 X 2 lenslet array for interconnection, allowing for a very simple and compact optical system. In addition to the holograms, the only other components necessary to complete the optical system are a polarizing beam splitter, two quarter-wave retardation plates, and a spacer. All of the optics are aligned and packaged into a single unit that is remarkably compact: 12.7 X 32.2 mm, weighting only 8.3 g.

A vertical-cavity surface-emitting laser (VCSEL) based free- space parallel optical interconnect is presented. The rigid optical link interconnects bi-directionally two PCBs over a distance of 3 inches. The 512 optical channels were grouped in 4 by 8 clusters on a 750-micrometers pitch, where each cluster is a 4 by 4 array of channels on a 125-micrometers pitch. Modules combining both microlenses and minilenses were used to propagate light from the VCSELs to the detectors. Details of the optical design and assembly process are presented.17

We present an architectural approach to overcome the interconnection problem of modern VLSI-circuits and demonstrate it experimentally in form of a multi-chip-module (MCM) in which four optoelectronic VLSI-chips communicate optically via a planar-integrated free-space optical system. The MCM implements a distributed parallel computing model and is compact and robust. The optical system has been integrated on the surfaces of a slab of quartz glass by means of lithographic microfabrication techniques. The quartz substrate also serves as circuit board for the opto- electronic VLSI-chips. Our approach allows dense packaging (> 100 per mm²) of large numbers of optical interconnects.

The specification of an optoelectronic switching module suitable for a packet router is presented. The module has a throughput of 500 Gb/s and will be the building block for a larger switch with a throughput of 131 Tb/s.

A new optical packet switching network and its enabling technologies are investigated for implementation in a Petaflops scale supercomputer system. We capitalize on the immense bandwidth of the optical fiber interconnects by deploying WDM/TDM packet payloads. To accommodate current optical switching technologies, the routing operations in the network are drastically simplified and the need for buffering is completely eliminated. This paper presents the experimental demonstration of the routing within the unique packet switched architecture. Multiple node hops are demonstrated in a node test-bed environment with a re- circulating loop configuration.

We have produced a prototype network-switch board (the RHiNET-2/SW) for optical interconnection. Eight pairs of 800-Mbit/s X 12-channel optical interconnection modules and a one-chip CMOS ASIC switch LSI (a 784-pin BGA package) are mounted on to a single board. This board allows 8- Gbit/s/port parallel optical data transmission over a distance of up to 100 m, and the aggregate throughput is 64 Gbit/s/board. All of the electrical interfaces are composed of CMOS-LVDS logic. We have evaluated the skew of the signal and the reliability of each optical port by measuring the BER. No errors were detected during the 10¹¹-bit packet data transmission at a data rate of 880 Mbit/s X 10 bits (8.8 Gbit/s/port). (This corresponds to a BER of less than 10^-11). The skew between data channels in one I/O port was less than 141 ps. The fiber length was 50 m. This test result shows that we achieved a high-throughput and long-transmission-length RHiNET-2/SW system using optical interconnection, and that the reliability of the I/O ports in the RHiNET-2/SW is sufficient for the RHiNET-2 parallel computing system.

We analyze the bandwidth needed for transmitting the addresses in future symmetric multiprocessor machines (SMP), constructed around a shared bus due to the critical obligation to preserve the coherence of the memory hierarchy. We show that an address-transaction bandwidth as high as several hundreds of Gbit/s will be necessary not to slow down the execution of most applications in large SMP's. This communication bandwidth seems incompatible with the operation constraints of shared electrical busses, making necessary the search for other implementations of the address transmission network. We consider the introduction of optical interconnects (OI) in this context. We review several solutions, in the ascending order of complexity of the optical subsystems as one critical issue concerns the degree of sophistication of the optical solutions and their cost. We first consider simple point to point OI's for a SMP chipset. The interest for OI's comes from the low energy consumption and from the possibility, in the future, to integrate several thousands of optical input/outputs per electronic chip. The we consider the implementation of an optical bus that is a multipoint optical line involving more optical functionality. We discuss the possibility of multiple accesses to the bus, and the constraints related to the necessity to maintain the coherence of caches.

The system architecture and the first prototype demonstrator system for the VCSEL-based Interconnects in VLSI Architectures for Computational Enhancement (VIVACE) program is described. The main goal of the VIVACE program is to build a high bi-section bandwidth free-space optically interconnected switch and to demonstrate it in a system of multiple compute nodes running a distributed algorithm. The prototype demonstrator system developed is a stand alone first-generation VIVACE Optical Network Interface Card (VONIC) communicating to another VONIC through a parallel- data fiber link. This system was developed to test the signal integrity and Bit Error Rate between two VONICs.

The development of a truly smart camera, with inherent capability for low latency semi-autonomous object recognition, tracking, and optimal image capture, has remained an elusive goal notwithstanding tremendous advances in the processing power afforded by VLSI technologies. These features are essential for a number of emerging multimedia- based applications, including enhanced augmented reality systems. Recent advances in understanding of the mechanisms of biological vision systems, together with similar advances in hybrid electronic/photonic packaging technology, offer the possibility of artificial biologically-inspired vision systems with significantly different, yet complementary, strengths and weaknesses. We describe herein several system implementation architectures based on spatial and temporal integration techniques within a multilayered structure, as well as the corresponding hardware implementation of these architectures based on the hybrid vertical integration of multiple silicon VLSI vision chips by means of dense 3D photonic interconnections.

In this paper, we propose a unified approach for the multicriteria design of diffractive optics. A multicriteria version of the Direct Binary Search that allows the user to tune the compromise between diffraction efficiency and Signal to Noise Ratio already exists. This technique proves extremely powerful but also very time consuming. We extend this multicriteria approach to IFTA, which permits to dramatically reduce the computation times, especially for multilevel domains.

Computer Aided Design (CAD) tools for modeling optical computing systems use a variety of different optical propagation techniques. However, for modeling micro-systems, common optical modeling techniques are not always valid. This paper discusses various optical propagation models for optical micro-systems by examining the requirements imposed by the physical size of the microsystems and the goal of achieving an interactive CAD framework. Based on these constraints, an appropriate optical model is chosen and used in our opto-electro-mechanical CAD tool, Chatoyant, to perform simulations of 2 X 2 micro-optical switch systems.

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by using the digital hologram of the key. This security technique is useful for secure storage and data transmission. Experimental results are presented to demonstrate the proposed method.

A digital volume holographic database in iron-doped lithium niobate to be read out by a multi-wavelength signal in the near infrared is here successfully performed, thanks to so- called two-color technique. Three 4-bit digital words have been recorded via angle multiplexing at 488 nm and retrieved at 1550 nm by a 200 GHz-WDM (Wavelength Division Multiplexing) beam.

This paper demonstrates a space integrating optical implementation of a single-layer FIRNN. A scrolling spatial light modulator is used for representing the spatio-temporal input plane, while the weights are implemented by the adaptive grating formation in a photorefractive crystal. Differential heterodyning is used for low-noise bipolar output detection and an active stabilization technique using a lock-in amplifier and a piezo-electric actuator is adopted for long term interferometric stability. Simulations and initial experimental results for adaptive sonar broadband beamforming are presented.

In this paper we describe the realization and the operation of a high capacity optoelectronic neural network implementing a classification of vectors through a Kohonen topological map. The setup uses volume holographic interconnects inside a photorefractive crystal to implement the neurons. We show that the system work and is able to classify several tens of vectors.

We constructed a learning optical neural network with variable learning coefficient by fuzzy controlling. The system performs learning with 2D optical means for handling images without scanning and pixeling. By the fuzzy controlling theory, the learning coefficient in back- propagation algorithm is adjusted based on the training error and training time. The effectiveness of the system confirmed by the learning experiments of the recognition of three human faces.

A coherent lightwave neural network system has been constructed for the first time. The novel system deals with phase and amplitude information consistently. Experiments demonstrate that complex-amplitude signal vectors embedded in its neural connections are recalled successfully. The coherent networks are expected to realize various attractive neural features such as carrier-frequency domain parallelism and self-organization of activeness mechanisms. The reported results can be a milepost toward such future highly functional neural network architecture and hardware.

The method of spatial mapping in biology vision field is applied to artificial neural networks for pattern recognition. By the coordinate transform that is called the complex-logarithm mapping and Fourier transform, the input images are transformed into scale- rotation- and shift- invariant patterns, and then fed into a multilayer neural network for learning and recognition. The results of computer simulation and an optical experimental system are described.

In this paper, we propose a foundry fabricated hybrid VCSEL- based GaAs smart pixel devoted to high speed and low cost optical interconnections. The device has an optical gain of 10.4 dB for power consumption less than 1 W. Moreover, the -3 dB bandwidth is suitable for transmission rate up to 6 Gbit/s.

Massively parallel optical interconnects are appropriate to ease the data bandwidth bottleneck that will occur in future computing applications. Vertical cavity surface emitting lasers (VCSELs) are promising sources for emerging 2D optical systems such as free space and guided wave optical interconnects. We discuss the development of high performance VCSEL arrays, including individually addressable and matrix addressable arrays. We also show the characteristics of GaAs microelectronic driver and photoreceiver chips that have been designed to interface with Si-based CMOS circuitry. Finally, the potential of these source and receiver modules for use in free space or guided wave parallel channel optical interconnect architectures will be described.

This paper presents the results of simultaneously working fully-differential optoelectronic receiver fabricated in Si CMOS with digital SIMD microprocessor on the same die next to analog, optical interface circuitry, the receiver have been hybrid integrated with a thin film InP-based inverted (I)-MSM photodetector and optically tested using external light source modulated by digital input signal. The noise immunity to mixed-signal digital switching noise of the differential receiver has been shown to be good enough to generate 10^-9 BER.

We present a digital smart pixel array, a new type of smart pixel array, for high speed parallel image processing. We have developed assembly methods for the device and fabricated 8 X 8 and 2 X 2 digital smart pixel arrays. We have also cascaded the 2 X 2 arrays, and demonstrated the functions of the device. Operation of the array can be changed by external instructions and basic operations, including data transmission between nearest neighboring pixels, were implemented. The operating speed in the cascaded system was 0.5 ms/frame.

Free space optical interconnects can increase throughput capacities and eliminate much of the energy consumption required for `all electronic' systems. High speed optical interconnects can be achieved by integrating optoelectronic devices with conventional electronics. Smart pixel arrays have been developed which use optical interconnects. An individual smart pixel cell is composed of a vertical cavity surface emitting laser (VCSEL), a photodetector, an optical receiver, a laser driver, and digital logic circuitry. Oxide-confined VCSELs are being developed to operate at 850 nm with a threshold current of approximately 1 mA. Multiple quantum well photodetectors are being fabricated from AlGaAs for use with the 850 nm VCSELs. The VCSELs and photodetectors are being integrated with complementary metal oxide semiconductor (CMOS) circuitry using flip-chip bonding. CMOS circuitry is being integrated with a 32 X 16 smart pixel array. The 512 smart pixels are serially linked. Thus, an entire data stream may be clocked through the chip and output electrically by the last pixel. Electrical testing is being performed on the CMOS smart pixel array. Using an on-chip pseudo random number generator, a digital data sequence was cycled through the chip verifying operation of the digital circuitry. Although, the prototype chip was fabricated in 1.2 micrometers technology, simulations have demonstrated that the array can operate at 1 Gb/s per pixel using 0.5 micrometers technology.

Research and development project of an indoor laser radar communication system has been going on to establish one of wireless communication network environments. In the project, corner-reflecting laser communicating target `the Hyper Versatile (HV) target', is used for a free-space laser data communication with low power consumption and for accurate position detection of the target. Reflective-type Liquid Crystal Spatial Light Modulator (LC SLM) is a possible attractive component of the HV target to solve the above subjects. The indoor laser radar system should operate at eye-safe wavelength region, however, no infrared operating SLM has been released because conventional SLMs have been designed and manufactured only for visible light operations. In this paper, infrared (1.06 micrometers ) operating Parallel Aligned nematic Liquid-crystal Spatial Light Modulator (PAL- SLM) is described for an application for the indoor laser radar system. Characteristics of the SLM and numerical simulations for corner-reflecting operations are indicated.

We propose a brief overview of different techniques to implement complex-valued filters on binary spatial light modulators (SLMs), including encoding techniques at both pixel- and cell- (i.e. group of pixels) levels. We show that group-oriented methods offer extended coding domains, at the expense of a reduced space bandwidth product and spurious noise in the correlation plane. We propose the concept of a time multiplexing technique that combines at the pixel level the pseudo-random encoding method with the minimum Euclidean distance approach. This pixel-oriented method offers the advantage to keep the full space bandwidth of SLMs, and the possibility to very efficiently encode ternary filters (-1, 0, +1) on binary phase (-1, +1) SLMs. Tested on a sequence of images acquired with an IR sensor in a tracking scenario (1 target), encoded ternary filters have offered superior performance in terms of peak-to-clutter ratio than classical BPOF (+45% in the simulation, +35% in the first optical experiments).

It is our goal to demonstrate the viability of massively parallel optical interconnections between electronic VLSI chips. This is done through the development of the technology necessary for the realization of such interconnections, and the definition of a systems architecture in which these interconnections play a meaningful role. Field-programmable gate arrays (FPGA) have been identified as a class of general-purpose very large scale integration components that could benefit from the massive introduction of state-of-the-art optical inter-chip interconnections at the logic level. In this paper, we present the realization of a small-scale optoelectronic FPGA with 8 X 8 logic cells, containing two optical sources and two receivers per FPGA cell yielding a total of 256 links per chip. These FPGA chips designed to operate with information rates of 80 Mbit/s/link will be used in a three- chip demonstrator system as a test bed for the concepts above. We first identify the reason why we think optical interconnects can provide added value in FPGAs. The next sections briefly discuss the general architecture of our demonstrator system and the realization of the optoelectronic FPGA. We then present first measurement results followed by ongoing work and conclusions.

The Optically Programmable Gate Array (OPGA), an optical version of a conventional FPGA, benefits from a direct parallel interface between an optical memory and a logic circuit. The OPGA utilizes a holographic memory accessed by an array of VCSELs to program its logic. An active pixel sensor array incorporated into the OPGA chip makes it possible to optically address the logic in a very short time allowing for rapid dynamic reconfiguration. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module can be made compact. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and database search.

In order to provide a reliable optical link, the emitters and detectors within a free-space optical interconnect need to be aligned to each other within tight tolerances. Typical methods to achieve this alignment involve the use of precision optomechanics or active steering elements. An alternative approach to the alignment problem is to use spatial redundancy. One way to accomplish this is by increasing the number of possible optical links and using only a subset of those links to provide reliable high-speed channels. This paper presents the design and testing of a high speed transmitter chip developed for an adaptive redundant optical interconnect system. Optoelectronic design and device packaging will also be described.

We propose and quantify a future role for photonic crystals in optical signal processing. We analyze the optical signal processing functionality of nonlinear periodic structures. By elaborating an analytical model and employing numerical simulations, we explore the performance of proposed devices. We prove that the proposed limiters provide true limiting by clamping the transmitted intensity at a level which is independent of the incident intensity. We explore the response of optical switches for signal and pump beams having the same and different frequencies. We describe and quantify the performance of the proposed structures in the realization of optical hard-limiters. We explore the performance of an all-optical logic gate whose forward- directed output implements a binary AND and whose backward- directed output implements an OR function. In addition we prove that the for fabrication errors as large as 10%, qualitative device functionality remains, with performance only modestly degraded.

The extraordinary increase of digital image contents requires the development of methods to classify or quickly search video sequences in movie databases. In this paper, we suggest a novel algorithm based on Eigen value decomposition to construct and search video databases, and that can be implemented using smart pixel optoelectronic systems. By successive iterations the images are progressively classified in sets and subsets in a tree-type configuration. To evaluate this method, a movie containing 2,262 frames has been analyzed, and a successful classification of these images in function of their contents was obtained. The realization of this algorithm on a smart pixel system called OCULAR-II is also discussed, and a demonstration of the database search algorithm on the OCULAR-II system is described.

In this paper, we propose the enhancement technique of the storage density in the disk-type memory with photorefractive cross polarized four-wave mixing. We calculate the amounts of shift that enable us to distinguish adjacent signals in the directions of the circle and the radius of the disk, and we carry out experiments to verify the analytical results. Also we investigate the temporal property of cross polarized four-wave mixing to estimate the optimum exposure time.

Sol-gel derived silica glasses are well suited as host for molecular dopants that show specific optical properties, such as laser action (high second and third order nonlinear coefficients). Such materials are of interest in optical waveguide and switching for telecommunication networks. The material is prepared by sol-gel technique in which some nanocrystallites of semiconductor (II-VI) are included, specially CdTe. Nanocrystallites are prepared out of the host matrix and included in the sol-gel after. The nanoparticles are prepared by sono-electrochemical technique. Sono-electrochemistry, or pulsed electrodeposition in presence of high intensity ultrasound, is used to product powders. The nanoparticles are characterized by scanning and transmission microscopy, electron diffraction, and x-ray fluorescence. The nonlinear refractive index and absorption are measured by the Z-scan method at 532 nm (Nd-YAG pulsed laser).

Substrate-mode gratings are used to couple and influence the signals that propagate in planar-integrated optical systems. Volume holograms are especially well suited for this role because they allow the recording of slanted fringe gratings. Photopolymer are among the best candidates for such applications due to easy handling, dry development process, high diffraction efficiency and replication possibilities. In this paper, we investigate the recording dynamics of Omnidex^TM photopolymer from DuPont. We use the theoretical diffusion model proposed by Zhao and Mouroulis in order to simulate the recording process. Two different experiments are described that lead to the quantitative determination of kinetic parameters in this material. These values are introduced in the diffusion model and different recording procedures are simulated. The conclusion shows that it could be valuable to let the material in the dark for several minutes before develop it. This investigation should improve the understanding of recording process and consequently it should permit to build more efficient components.

In many applications, it is necessary to evaluate the beam parameters of the basis Hermite-Gaussian functions which are used to decompose a given laser beam. This paper compares two methods for estimating the beam parameters, both of which are based on intensity measurement. One is an exact optimization method, which can find the optimal beam parameters but has high computational demands. The other is a moment method which requires less computation but only yields approximation to the optimal beam parameters and whose application is limited to beams close to Gaussian or a mixture of incoherent Hermite-Gaussian modes. It is found that the moment method can provide sufficiently accurate results in certain circumstances.

Spatio-temporal pulse shaper which controls the spatial and temporal profile of an ultrafast light pulse. The pulse shaper uses the spatio-temporal coupling effect in a pulse shaper. In this paper, the quantitative property is analyzed numerically by using Wigner distribution function. By the analysis, it is confirmed that spatio-temporal output pulse track forms the differentiation of the phase mask.

We present a novel method for achieving in real-time a 2D object wavelet decomposition with white light illumination. The underlying idea of the suggested method is wavelength multiplexing: the different wavelet components of an input object are transmitted simultaneously in different wavelengths and summed incoherently at the output plane. Experimental results show the utility of the new proposed method.

Recently, optical waveguides implementation on the substrate has been developed due to the requirement for large capacity and high-speed transmission. Considering that an optical circuit on the substrate must be assembled in a limited space, the integration of the circuit is one of the most important issues for the design of the optical circuits. In optical circuits, a Y-branch waveguide is a basic element of circuits and the length of the Y-branch waveguide depends on its branch angle. To achieve the high density integration of optical circuits, a wide angle Y-branch module, which is a small module, is highly desired. In this paper, we propose a new Y-branch waveguide using reflection at the inclined side-wall of the waveguide. The results of the numerical analysis show the efficiency of the proposed Y-branch waveguide, namely low-los and wide branching, in optical waveguide. Moreover, this paper also discuss that the proposed model is tolerable to the fabrication error comparing to the conventional Y-branch waveguide.

In this study we analyze the optical propagation properties due to the roughness of side walls in waveguides (core regions), which is inherent in the patterning processes such as RIE, UV curing and so on. In the analysis we evaluate the increase in loss due to the side-wall roughness, where the width of waveguides vary sinusoidally and randomly in the models. As a parameter, we pay attention to the relative refractive index different between the core and clad regions. The Finite-Difference Beam Propagation Method is used in the simulation. It is found that the increase in loss depends on the period varied in waveguides and the maximum value of loss is about 0.2 dB/cm in present conditions. However the large value of loss more than 1 dB/cm appears noticeably in some specific periods, and this is discussed using the Brillouin diagram.

We propose an optical demodulator with photorefractive cross-polarized duplex two-wave mixing, in which the phase- modulated signal beam is converted into the intensity- modulated output signal beams. We calculate the intensity variations of the output signal beams when phase-modulated signal beam input to photorefractive cross-polarized duplex two-wave mixing.

We report on experimental and theoretical studies of linear electrooptic (Pockels) coefficients in push-pull chromophores incorporating the 1,3-dithiol-2-ylidene moiety as the electron donating. The proposed theoretical approach is based on molecular dynamics geometry optimization and quantum chemical calculations of the appropriate molecules. Intermolecular interactions are taken into account within a framework of solid state local density approximation. The quantum chemical method is based on a self-consistent norm- conserving nonlocal pseudopotential with orthogonalization to the core pseudo-wavefunctions by linear combination of atomic orbitals. Contribution of the electronic and ionic parts into the output electrooptic tensor component r₁₁₁ ((lambda) equals 633 nm) is evaluated. An enhancement of heteropolar molecular ionicity leads to an increase of the resulting r₁₁₁ electrooptic coefficient. Vibration (ionic) and electronic modes are found to be sensitive to substitution of the side chemical groups. The dominant role of some particular chemical fragments dominating in the observed coefficients is really evident.

We report large third-order nonlinear optical susceptibilities (chi) ^<3>_ijkl of new tetrathiafulvalene (TTF) derivatives, using the degenerate four wave mixing (DFWM) method. To know the physical origin of their optical nonlinearities, we separate electronic and ionic contributions to nonlinear optical susceptibilities. The electronic contribution to the third-order nonlinear optical susceptibilities of the studied molecules is dominant. From DFWM measurements we also deduce values of the third-order hyperpolarizabilities (chi) which are about 10⁵ greater than the (chi) value for CS₂. We have thus shown that the molecules under consideration posses larger third order nonlinear optical susceptibilities compared to the polyazine derivatives, acetylenic analogues of TTF and to the ethylenic TTF derivatives. All theoretical simulations are done within a framework of semi-empirical quantum chemical calculation. A correlation between molecular dipole moments and third order susceptibilities is found.

In this paper we describe the fabrication of an array of integrated cylindrical microlenses on top of a single GaAs MSM photodetector. Experimental data shows an increase of about 65% on the photocurrent of the MSM photodiode as a result of the improved optical coupling efficiency.

This paper presents a study of the effects of the accumulation of positioning errors across multiple optical components (also named `tolerance stackup') on the optical power throughput performance of free-space optical interconnects. It is shown that a sensitivity analysis is not adequate to establish a tolerance budget as it provides no information regarding the system yield upon assembly. The effects of tolerance stackup across a system are more severe than a statistical root-sum-square type analysis predicts. It is demonstrated that errors accumulate linearly with interconnect length.

This paper addresses the issue of alignment in free-space optical interconnects by investigation optical configurations that are inherently tolerant to misalignment. This is done by evaluating different designs for a module which integrates an optoelectronic-VLSI chip with one or two lens array components. The designs are compared using a common set of system parameters and closed-form analytical expressions are derived for misalignment tolerances and system scalability. It is shown that the alignability of a module can be adequately specified by the product of its lateral and tilt misalignment tolerance and this product is an invariant of the system. Misalignment-tolerant configurations are identified and general design guidelines are formulated.

The FAST-Net (Free-space Accelerator for Switching Terabit Networks) concept uses an array of wide field-of-view imaging lenses to realize a high-density shuffle interconnect across an array of smart-pixel integrated circuits. This paper presents a design approach for these lenses that achieves the minimum complexity required to meet the demands of the FAST-Net concept's off-axis multi-chip environment. Generalized eikonals for arbitrary surfaces were examined to determine the performance bounds for the FAST-Net optical system. Then an analysis provided an estimate of 6 for the number of spherical surfaces needed to achieve good optical resolution and distortion performance across an array of 10-micron diameter VCSEL sources that are imaged onto a array of 50-micron wide detectors. A ray trace simulation confirmed this number. Subsequent analysis evaluated the achievable efficient of replacing spherical surfaces with aspherical ones. By exploiting the mismatch between the low numerical aperture VCSELs and relatively higher numerical aperture interconnection optics, it was found that 3 aspherical surfaces could replace 6 spherical surfaces in the FAST-Net system for the specified performance criteria. A lens design that utilizes 3 aspherical surfaces and achieves necessary registration and resolution of the FAST-Net system was determined. The results provide a general framework for the design of wide field-of-view free space interconnection systems that incorporate high-density VCSEL arrays.

The theory of the diffraction of plane waves on an extended Fabry-Perot interferometer with a phase sinusoidal diffraction grating built-in inside the interferometer is proposed. The theory is constructed on the basis of Maxwell equations in approximation of non-absorptive media. The examples of calculation of distribution of light fields of thin-film interferometers are given in view of all possible orders of a diffraction in a transmission and reflection. It is shown that the properties of investigated systems essentially differ both from properties of interferometers and from properties of the usual holograms without reflecting coatings.

In this study, new designs not using electronic circuits are suggested for an optical vector multiplier to achieve optical interconnections. Nonlinear optical devices using photorefractive four-wave mixing are employed as the core device. If optical interconnection can be directly controlled by light, self-routing at an optical ATM can be realized without using electronic circuits. It is highly advantageous for suppression of heating or achieving high density interconnection. The concepts and optical designs of an all-optical interconnection and a self-routing system are presented here and basic operations in experimentation are examined.

Both theoretical and experimental analysis is carried out of dynamics describing the information data transfer over the ring by means of switching waves propagating in the plane of bistable layer in direction that is perpendicular to the direction of control and information laser beams. The design and experimental realization is reported of all-optical planar loop circuit demonstrator based on the nonlinear thin-film semiconductor interferometer in the framework of transverse `lock-and-clock' architecture. All-optical and optoelectronic `planar-free space' circuits of such kind can be used for the development and construction of optical systems for digital (and analog) processing, transfer and spatial switching of light information signals.

Next generation high-speed pc board interconnects will be based on integrated optical multimode waveguides with cross- sectional sizes comparable to those of electrical microstrip lines. The design of such interconnects requires appropriate simulation models of the multimode waveguides and the laser- and photo-diodes, as well. Since single-mode interconnects can be modeled very efficiently by well known numerical methods such as FEM and BPM, these methods are not applicable for optical multimode waveguides with more than 1000 propagating modes. Due to the numerical complexity only methods based on geometrical optics, called ray tracing, can be applied efficiently. This paper deals with a time domain modeling and simulation approach for analyzing the signal behavior of multimode waveguide based electrical-optical interconnection systems as a whole. Modeling of multimode waveguide components as well as macromodeling of laser- and photo-diodes is explained in detail. The modeling approaches are discussed by examples.

The principles of the photonic integration of proposed 2D switching networks are presented which is mainly based on the utilization of planar integration techniques and their development. This `sandwich' technique composes layers of planar integration with the major goal of minimizing (1) the number of interconnections between adjacent layers with slopes (2) the number of crossing waveguides within single layers and between adjacent layers and of optimizing (3) the number of layers. This is a multi-level optimization problem whose first step can be solved by utilizing the symmetry of the 3D architectures. The presented work explains concepts and prepares their geometry for the ongoing physical analysis. The presented architectures are restricted to passive switches, capable to provide e.g. all-optical logic circuits. Hints for an extension towards active switches are also briefly presented.

In this paper, we present a low cost fiber-optic data link for the computing cluster. The link is a 32 bit-virtual- channel fiber-optic computer bus used only a pair of OE devices and fibers. The link is integrated with the popular PCI Bus interface in order to make the link hold the same bandwidth as that of the PCI Bus, and it can operate under managed by PCI Bus. Our research addresses how to match accessing bandwidth between computer bus and high-speed optical interconnections, and how to make low overhead and latency interfaces between optics and electronics, and integrates fiber optic link into computing system designs.

This paper investigates different factors that influence the channel density of signals propagated through fiber imaging guides. These include the uniformity of the optical power transmitted through the guide, the geometrical structure of the guide, the optical crosstalk to adjacent signal channels, and modal noise. A model for the power uniformity and optical cross-talk is provided and is used to evaluate the channel density of different coupling modes. A commercially available fiber image guide is evaluated in the context of these density considerations and is experimentally tested. Modal noise is also experimentally measured for different coupling conditions to the fiber- imaging guide. The resultant signal channel based on these criteria was found to have a diameter approximately 3 times the center spacing of the fiber elements in the fiber imaging guide. This density compares favorably with electrical interconnect densities that are projected for tape automated bonding and flip-chip bonding techniques.

An optical packaging scheme based on alignment-free optical modules for free-space interconnection is presented. Solder- bump-bonding technique is introduced to achieve precise self-alignment in free-space optical system. The proposed method is verified by experimental fabrication of optical modules.

Board to board free-space optical interconnects can deliver high bandwidth with no physical contact but suffer from poor tolerances to misalignment. In order to obtain high misalignment tolerances, we propose the use of an active alignment scheme in conjunction with an optimized optical design. The active alignment scheme uses a redundant set of optical links and the active selection of the best link. The optical design maximizes the alignment tolerances between the two boards.

This paper presents the design of a receiver used in a self- aligning optical interconnect. We have made use of spatial redundancy to increase the misalignment tolerance of a system of four 1 Gb/s free-space optical links. The receiver for this system is a rapidly re-configurable array that accepts nine low-amplitude, high-speed photocurrents, selects one of them, and then outputs that signal as a digital differential positive emitter coupled logic signal. The selection of which channel to amplify is based on received power, and is performed off-chip. Preliminary results indicate that the receiver performs with a low bit error rate up to 750 Mb/s.

A compact image capturing system called TOMBO (thin observation module by bound optics) is presented, in which a compound-eye imaging optics is utilized for very thin system configuration. The captured multiple images are processed to retrieve the object image. An experimental system was constructed for verifying the principle and clarifying the issues related on the implementation. For the retrieve, two kinds of processing are considered: simple sampling and back projection methods. The TOMBO system is an instance of opto- electronic hybrid system providing excellent features based on opto-electronic cooperation.

We report about ongoing work on a free-space optical interconnect system, which will demonstrate a Fast Fourier Transformation calculation, distributed among six processor chips. Logically, the processors are arranged in two linear chains, where each element communicates optically with its nearest neighbors. Physically, the setup consists of a large motherboard, several multi-chip carrier modules, which hold the processor/driver chips and the optoelectronic chips (arrays of lasers and detectors), and several plug-on-top optics modules, which provide the optical links between the chip carrier modules. The system design tries to satisfy numerous constraints, such as compact size, potential for mass-production, suitability for large arrays (up to 1024 parallel channels), compatibility with standard electronics fabrication and packaging technology, potential for active misalignment compensation by integration MEMS technology, and suitability for testing different imaging topologies. We present the system architecture together with details of key components and modules, and report on first experiences with prototype modules of the setup.

2D Parallel Optical Interconnects are capable of providing large connectivity between elements in computing and switching systems. Using this technology we have demonstrated a bi-directional optical interconnect between two PCBs containing optoelectronic VLSI circuits. The OE- VLSI circuits were constructed using VCSELs and photodiodes flip-chip bump bonded to a 0.35 micrometers CMOS chip. The CMOS was comprised of 256 Vertical Cavity Surface Emitting Laser (VCSEL) drivers, 256 receivers, and the requisite buffer and control circuits required to operate the large transceiver array. This is the first system, to our knowledge, to send bi-directional data optically between optoelectronic VLSI chips which have both VCSELs and photodiodes co-integrated on the same substrate.

We present a networking and signal processing architecture called Transpar-TR (Translucent Smart Pixel Array-Token- Ring) that utilizes smart pixel technology to perform 2D parallel optical data transfer between digital processing nodes. Transpar-TR moves data through the network in the form of 3D packets (2D spatial and 1D time). By utilizing many spatial parallel channels, Transpar-TR can achieve high throughput, low latency communication between nodes, even with each channel operating at moderate data rates. The 2D array of optical channels is created by an array of smart pixels, each with an optical input and optical output. Each smart pixel consists of two sections, an optical network interface and ALU-based processor with local memory. The optical network interface is responsible for transmitting and receiving optical data packets using a slotted token ring network protocol. The smart pixel array operates as a single-instruction multiple-data processor when processing data. The Transpar-TR network, consisting of networked smart pixel arrays, can perform pipelined parallel processing very efficiently on 2D data structures such as images and video. This paper discusses the Transpar-TR implementation in which each node is the printed circuit board integration of a VCSEL-MSM chip, a transimpedance receiver array chip and an FPGA chip.

Optical pattern recognition can be improved using powerful filters or defining new correlations. The morphological correlation is a robust detection method that minimizes the mean absolute error between two patterns. The morphological correlation is a nonlinear correlation and it is defined as the average over all the amplitudes of the linear correlation between thresholded versions of the input scene and the reference object for every gray level. This nonlinear correlation can be implemented optically using a joint transform correlator and provides higher performance and higher discrimination abilities in comparison with other linear correlation methods. We define different morphological correlations using different binary decompositions. Those correlations allow efficient pattern recognition with higher discrimination ability than other common linear image detection techniques. Experimental result will be presented.

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.

In recent years there has been a great deal of interest in the use of optical interconnection techniques within a digital electronic circuits. The Semiconductor Industry Association has highlighted the necessity of the optical approach in "The National Technology Roadmap for Semiconductors" in 1997 [1]. The availability of large space-bandwidth product, together with the potential inadequacies of copper, have usually been cited as the main advantages of optics over its electronic alternatives for interconnection applications. As more advanced and high density photonics devices in 2D format have been developed, the need for more advanced micro-optical components that allow the manipulation of light from, and interconnection between these arrays of devices in the third dimension, has grown with it. The rapid development of the field of diffractive optics (i.e. digital holography) and other micro-optical fabrication technologies over the past 20 years has to a major extent been motivated, and influenced by the requirements mentioned above. These elements have been able to provide solutions to problems, where conventional bulk optics offer no (elegant) solutions. They have proven to be particularly successful in providing fan-out, fan-in and optical interconnections of nonlocal and global permutations. [See ref. 1 and references therein]. The availability of more advanced fabrication technologies, similar to those in VLSI manufacturing, has allowed these surface-relief elements to become more efficient, easily reproducible and have more complex functionality. Here a number of available technologies for realising these optical interconnects will be described. I will primarily concentrate on the design, fabrication and applications of surface relief structures as well as refractive microlens arrays for use in a number of interconnection and switching systems. In addition, the role and advantages offered by diffractive microstructures in precise alignment of opto-electronics device arrays with micro-optical components, that are required for beam shaping in system applications, will be discussed [2-4].

In this work, we elaborate on the compromise between the efficiency of a multiprocessor computer architecture for handling large classes of computing tasks and the good performance of optics for implementing shift invariant operations, in particular convolution. We derive a class of processors, optoelectronic cellular automata, that can efficiently implement intensive, low level vision tasks in a time compatible with application constraints up to standard video rates. As one illustration, a parallel simulated annealing task performing motion detection on an image sequence is demonstrated.

Cost-effective optical correlators are now available for industrial applications. One such application field is the real-time automatic inspection of textile web, in which the high data throughput of the optical correlator over-performs that of the electronic computer. Two approaches for defect enhancement using of wavelet and Wiener filters are proposed. The band-pass wavelet filter is designed to give higher weights in the frequency band, where the energy of defect is higher than that of the web, and to suppress the zero, first and all higher diffracted orders. The Wiener filters are designed based on an average defect shape, with the web texture considered as noise. Using the technique developed at INO (National Optics Institute), a set up of the Vander Lugt type correlator demonstrates experimentally the relevancy of the algorithms. Simulation and optical results are presented.

Coherent light is the most popular carrier of a signal in an optical information processing system. The matched filtering system (Van Der Lugt 1965) is a prominent example. However, coherent optics is experimentally delicate, not well suited for unfriendly environments. As a reaction to this dilemma some new systems, that use totally incoherent light, have been presented recently. Those systems work reasonably well. But they can handle only real-valued non-negative signals, directly. An alternative approach is to use partially- coherent light. Now the optical system is not anymore as fragile as a coherent system. And the signals, which are now implemented as coherence functions, can be complex, in contrast to incoherent optics. However, the hardware of partially coherent systems is more elaborate.

We present a device that is capable of switching a sequence of equally space pulses between two or more outputs, according to the switching information carried from the first pulse, that behaves as an addresser. The device acts as an all-optical router and it is based on the properties of a soliton beam in a transverse refractive index profile. We further study the interaction force between solitons.

Electrophoresis is a classical electrochemical transport process, which is based on the migration of charged particles in a suspension by the influence of an electric field. One of the important applications of this technique is the study of DNA/RNA hybridization on bio-electronic chips. However, electrophoretic pick and place techniques are currently limited to the serial `pick' and `place' of individual devices or materials. There is a need for the rapid and parallel pick-and-place of individual devices to particular locations on a host substrate. In this paper, we present a novel electrochemical system for non-lithographic, field assisted, fluidic pick and place assembly of devices on a silicon substrate by means of electrical and optical addressing. The methodology presented here can be applied to massively parallel assembly of large semiconductor arrays (> 1000 X 1000) with fast (approximately a few seconds) and accurate positioning for a wide range of device sizes (0.8 - 100 micrometers ).

The existing mismatch between the bandwidth capacity of optical fiber and electronic devices, can be used to increase the speed, provide security and reliability in the transmission and distribution of information. To implement these applications, all-optical multiplexer performing space-to-time (i.e., parallel-to-serial) transformation at the transmitter and demultiplexer performing time-to-space (i.e., serial-to-parallel) transformation at the receiver will need to be constructed. For efficient bandwidth utilization, these processors need to be operated at rates determined by the bandwidth of the optical pulses. Ultrashort pulse laser technology has recently experienced significant advances, producing high peak power waveforms of optical radiation in the femtosecond duration range. These ultrafast waveforms can be synthesized and processed in the temporal frequency domain by spatially dispersing the frequency components in a spectral processing device (SPD) and performing operations on the spectrally decomposed wave (SDW). Space-to-time multiplexing via waveform synthesis using SDW filtering has been demonstrated with prefabricated masks, spatial light modulators and holograms. These filters are limited in their adaptability rate -a new filter can be implemented only as fast as the modulator response time or recording time ofa new hologram - typicallywell over a microsecond. To fulfill our goal of real-time SDW processing, we utilize a nonlinear wave mixing process based on four-wave mixing via cascaded second-order nonlinearities (CSN) in a 2)medium performed inside the SPD. The CSN arrangement consists of a frequency-up conversion process followed by a frequency-down conversion process satisfying the type-Il non-collinear phase matching condition. Our experiments are concerned with ultrafast information exchange between spatially parallel signals and higher bandwidth temporal signals. For the waveform synthesis experiment, we introduce two spatial information modulated waves carried by quasi-monochromatic light and a SDW of a ultrashort femtosecond pulse. The four wave mixing process produces a SDW that is a product of three waveforms: a spatial Fourier Transform (FT) of the two spatial information carrying waves and the SDW (i.e., temporal FT) of a femtosecond laser pulse. The spatial-temporal information exchange (i.e., the generated SDW) results in a synthesized waveform that is a time-scaled version of the spatial image, performed on a single shot basis with femtosecond-rate response time due to the fast nonlinearity. The inverse time-to-space transformation for detection of femtosecond pulse sequences is achieved using nonlinear three-wave mixing in a crystal. The two input waves are the SDW of a sequence of ultrashort pulses that need to be detected and a reference pulse. The nonlinear interaction between the two SDW's results in generating a quasimonochromatic second harmonic wave. The frequency ofthe second harmonic fields is twice the center frequency ofthe incident fields. The generated second harmonic fields contain spatial frequencies determined by the time delay between the reference pulse and the pulses in the signal. Thus a 1-D spatial FT of the second harmonic field produces a l-D spatial image equivalent to the temporal cross-correlation between the reference and the signal pulses. With short pulses, the spatial image has one-to-one correspondence with the signal pulse, implementing the desired time-to-space demultiplexing at femtosecond rates.

As silicon chips advance to future generations with higher densities of transistors and faster clock speeds, the problems with electrical interconnects to and on silicon chips become significantly worse. Even the most optimistic scaling models show that scaling the wiring down with the transistors leads to interconnects that do not keep up with the faster transistor speeds. The interconnect scaling problem is arguably even worse for connections off the chip. There are also increasing problems with signal integrity on electrical interconnects as speeds increase, including cross-talk between lines, signal distortion and attenuation, increasing need for voltage isolation, poorer timing of the signals, and generally increasing difficulty of design of the interconnect. There are electrical approaches to dealing with these interconnect problems, including changing architectures to avoid use of long interconnects, improving design tools to optimize the interconnect design more effectively, and improving signaling on electrical lines (such as using equalization). All of these will likely be used. Optics, however, arguably offers the only physical solution to the problem ofthe scaling difficulties of interconnects. Because of its different physics (specifically, the absence of electrical resistance phenomena) it avoids the various common problems of electrical interconnect scaling. It also naturally gives voltage isolation, and avoids most of the other signal integrity problems of electrical wires. Because the optics itself does not need to be redesigned as the clock rate is increased, it may make systems easier to design. Optical interconnects, however, do have their own problems. Especially, optical interconnection is an immature technology, leading to many issues, such as the following. It is impossible to reliably predict cost at the present time. The devices and optical components exist mostly in research laboratories. Integration with silicon is still difficult, though possible. Appropriate optomechanical technology for low-cost, convenient optical assemblies has not been developed. Issues still remain in reducing operating voltage of optoelectronic devices to match future silicon generations. It is not clear whether existing optoelectronic devices can meet the operating environment conditions of silicon circuits (e.g., temperature range) in practice. Receiver circuits with sufficient sensitivity, low enough power, and immunity to digital noise have not been sufficiently tested. There have been relatively few systems experiments to test optical interconnects in realistic conditions. Even the precise applications are unclear. The benefits of on-chip optical interconnects are still debatable (though the arguments for off-chip optical interconnects are relatively strong). This tutorial will examine these various arguments [1] —[4] for limitations on electrical interconnects and possibilities for future optical interconnect technology.

This tutorial reviews some concepts of pattern recognition and introduces some recent new ideas. After a brief overview of classical pattern recognition approaches, some unconventional and useful concepts will be introduced and used to show how the input formats of images for both digital and optical pattern recognition techniques influence the choice of methods and of criteria for measuring similarity. The importance of nonimearities and of pre-processing will be demonstrated, and the important differences between cases where the objects of interest may be segmented from the scene and those where they may not will be pointed out. It will be shown that the mathematics underlying conventional classification methods and those using neural networks are not as different as they may first appear, and that some tasks predicted for neural networks involving pattern classification are impossible in principle. Some new approaches for achieving object classification invariant under translation, rotation, illumination and other distortions will be discussed.

We present several methods for optoelectronic processing of 2- and 3-D images based in digital holography. 2D objects are optically encrypted by using on-axis digital holography. The digital hologram is obtained with phase-shifting interferometry. The encryption of the hologram is performed by using random phase codes. As conventional holograms, digital holograms contain information about shape, location and orientation of 3-D objects. This allows us to apply 3-D pattern recognition techniques with high discrimination. We also measure 3-D orientation changes using the information contained in digital holograms. Experimental results are presented.

Abstract not available.