Digital optical computing is gradually emerging as an important new technology. Optical computers have very different architectures from their electronic counterparts. They are potentially capable of combining processor and system level operations to obtain substantial reductions in overall software requirements. The most important aspect of these new computers is their interconnection capabilities. These capabilities are either directly or subtly re-sponsible for fusing processor and system level operations through features such as massive parallelism, reconfigurability, the ability to implement multiple-valued logic, and the ability to perform multiple-class discrimination.

Recent advances in optical bistability in a variety of materials and devices offer the potential for high speed operation over extended ranges of wavelength and temperature. The advantages of optoelec-tronic devices and multiple-valued logic are combined in various multistable solid-state device techniques, of which negative resistance multistability is most compatible with utilization of bistable optoelec-tronic devices. Additional stable states result from negative resistance interactions and facilitate implementation of variable radix analog and digital applications. Needed characteristics of bistable optical devices are outlined for compatibility with multiple-valued logic implementation. Multiple-valued optical logic offers synergistic potential for improved performance.

For some time now, authors of SPIE Proceedings papers have been receiving, as part of their author's kits, invitations to submit photocopies of their papers to the Editor of Optical Engineering to be considered for publication in that journal. These invitations inform the authors that their papers will be reviewed and, if accepted, that they must be retyped and submitted in the format required for Optical Engineering manuscripts. The invitations have not gone unheeded, and I have been literally deluged with such papers since I became Editor this past July. In fact, I have been receiving far too many submissions of Proceedings papers, and I would like to try to stem the tide.

Optical Radiation Measurements Vol. 5: Visual Measurements-Reviewed by F. Dow Smith; Industrial Lasers and Their Applications-Reviewed by Phil Hemmer; Robotics: A User-Friendly Introduction-Reviewed by John F. Gilmore; Principles of Phase Conjugation-Reviewed by Duncan G. Steel; Videodisc and Optical Memory Systems-Reviewed by Albert A Jamberdino

The state of the art for multiple-valued electronic devices relying on integrated injection logic (I2L) is discussed. Applications and extension of multiple-valued I2L devices to quaternary logic technology are presented.

The need for ultra-high-speed computing for a variety of modern processing problems has generated new interest in using truth-table look-up techniques. Further, due to the frequently parallel nature of these processing problems, optical systems appear to be promising for these applications. The basic principles of truth-table look-up processing are reviewed in this paper. The issues of number representation, multilevel coding, and logical minimization are discussed. Example fixed-radix and residue number representations are given with and without multilevel coding. Logical reduction techniques are discussed with examples. A comparison of the number of truth-table entries needed for 16-bit full-precision addition and multiplication is given, illustrating the advantage of the multilevel coded residue number representation.

The operating characteristics of digital optical computers utilizing spatial light modulator based shadow casting are reviewed. The geometric and physical limitations of this method are examined. Because of the highly parallel nature of this approach, such systems are capable of truth-table processing. A detailed analysis of the relative advantages of both direct and associative truth table processing is presented. For each case, the use of binary or of multiple-valued logic is considered. The respective merits from the point of view of the number of computations per second and the energy required per computation are outlined. Switching energy considerations based on the use of multiple wavelengths in these systems are also discussed. The characteristic features of this type of optical logic are compared to those of electronic logic.

Improving the precision of optically performed computations is a critical aspect of photonic computing. One possible method for improving precision is through the use of modified signed-digit (MSD) arithmetic. Optical implementation of MSD arithmetic offers several important advantages over other optical techniques such as the digital multiplication by analog convolution (DMAC) algorithm or the use of residue arithmetic. These advantages include the parallel pipeline flow of digits due to carry-free addition and subtraction, fixed-point as well as floating-point capability, and the potential for performing divisions. We present a brief description of the modified signed-digit number system and suggest one optical architecture for implementing MSD fixed-point addition, subtraction, and multiplication.

Computer simulation of thin film growth has been used extensively to gain insight into the origin and nature of the microstructure of vapor-deposited thin films. Usually, however, no attempts are made to predict film properties other than column angle and film density from such simulations. The aim of our work is to derive quantitative data from computer simulations in order to be able to predict relevant properties of optical coatings. The deposition of 2500 to 25,000 particles has been simulated on different computers by random deposition of two-dimensional hard disks, using a simple relaxation scheme. Statistical analysis of the results yields quantitative data for the density, column angle, and column period. On the basis of these results, a simple model has been developed for the microstructure of a three-dimensional film. The birefringence and the shape of water-penetration fronts in evaporated optical coatings, predicted from this model, are confirmed by experiment.

Multiple-valued logic, in which the number of discrete logic levels is not confined to two, as is the case with all present-day digital systems, has many theoretical advantages. Multiple-valued threshold logic has particular attractions but, as with all forms of logic with more than two logic levels, is presently constrained by the lack of good devices for system realization. In this paper we introduce the theoretical attractions of multiple-valued digital systems and look toward optoelectronics for more realistic devices in the future.

A new method has been developed to measure the modulation transfer function (MTF) of an array out to the Nyquist frequency without high quality optical or mechanical components, without precision alignment, and with only one moving part. Test results for an infrared staring array of PtSi Schottky barrier construction show that this technique is a viable MTF measurement approach in the 3 to 5 µm spectral region.

The characteristic features of deterministic and nondeterministic optical threshold logic gates are reviewed. Analog, binary, multiple-valued, multiple-class, and polynomial threshold gates are considered. Threshold synthesis techniques are outlined. Bulk optical and integrated optical implementations of reconfigurable threshold gates are discussed. Examples of deterministic logic operations involving binary addition and digital picture processing are presented. Applications to nondeterministic operations such as pattern recognition and heteroassociative processing are considered. The sensitivity of deterministic and nondeterministic mul-tiple-input optical threshold gates to physical errors is analyzed. The particular advantages of optically connected threshold gates with respect to electronic threshold gates are discussed.

Optical processing over the past 10 years has made significant advances in implementing a great number of digital pattern recognition algorithms. Especially important are optical implementations of digital algorithms that involve global operations on 2-D patterns. Such applications of optical processing will significantly speed up the response time of the pattern recognition systems while maintaining the reliability offered by digital methods. This paper summarily describes some of these advances, for example, in preprocessing, feature extraction, and statistical pattern recognition. It is proposed that a microcomputer-based hybrid system be developed in which digital implementations of algorithms involving neighborhood operations can be combined with optical implementations of algorithms involving global operations on 2-D patterns.

Many problems are efficiently computed on nearest neighbor connected machines because they involve regular grids or grids that may be envisaged as distortions from regular. Examples include image processing and finite differences and finite elements that dominate engineering and scientific computation. Previously, I proposed an optical nearest neighbor machine concept with 5-bit accuracy. The simple design in this paper uses residue number arithmetic and two deformable mirror arrays of 1000 x 1000 elements to achieve 15 million operations per second with 32-bit accuracy. I assume that an array may be set in 8 ms. Duplication of equipment by 64 times enables one billion operations per second because perfect parallelism is achievable with residue numbers and nearest neighbor concepts. It is anticipated that the increased use of deformable mirror devices in computer peripherals will advance the technology to the point where designs such as that proposed will be practical. The proposed scheme appears to be superior to outer product and optical modulo schemes for nearest neighbor computation.

A proposed high performance gigaflop signal processor is described in which 512 processors are interconnected with a 768 by 768 crossbar switch utilizing a spatial light modulator of the type presently under development at Texas Instruments. Optical fibers are used to provide high speed communication between the processors and the switch. The system, processor nodes, programming, and functional operation are described. The advantages are discussed for reconfigurability, optical crossbar switches, and programmed data flow. Efficient implementations are presented for a systolic filter, a fast Fourier transform, a correlator, and a matrix-vector multiplier. Preliminary performance estimates suggest that over one gigaflop performance is achievable for these algorithms on this processor.

The use of a new Sagnac interferometer switch (SIS) to perform digital optical logic is described. The optical logic switch consists of a Sagnac interferometer with an optical nonlinear material in its loop. Both the SIS input and output logic variables are optical pulses. The output SIS state is a function of the initial mirror alignment and the state of the inducing light beam. Using various SIS interconnections, all 16 two-variable binary logic functions can be implemented. Parallel logic processing of different logic functions can be performed using a single Sagnac interferometer. Since SIS elements are cascadable, sequential operation is also possible. As an example, an implementation of the SIS optical binary full adder is illustrated. If one input is a cw analog signal and another input is an ultrafast optical pulse train, the SIS can also be used as an ultrafast optical sampling device. Conditions for proper optical sampling frequency are presented.

Novel optical computing techniques based on shifting operations of an optical interference fringe are described. Architectures of optical processing systems in both the bulk and the guided-wave approach are discussed. The dividing of the shifted output fringe allows the parallel implementation of multiple logic gates. The multiple-output scheme is controllable in number and sort via a photorefractive effect. Representative examples of applications to an optical half-adder, binary multiplication, and vector-matrix arithmetic are given.

The use of stimulated light scattering as a means for achieving optical control functions directed toward an optical computer is described. Stimulated thermal Rayleigh scattering is seen to be a preferred nonlinear optical mechanism when compared with the more familiar stimulated Raman and stimulated Brillouin scattering. It possesses the highest gain, the lowest threshold, and scattered radiation that is approximately the same frequency as the inducing radiation. Optical control functions such as optical bistable switching, optical amplification, and optical limiting or clipping are described.

For future computer and information systems such as the Space Station data management system, the communication processing delays at the network nodes will become a critical issue. Exploiting recent advances in optical processing and integrated optoelectronics promises to solve the information delay bottlenecks. This paper outlines the results of a study to develop the functional concepts for an intelligent optical node incorporating as many optical signal processing elements as feasible.

Developing a reliable method for obtaining chemical information on components of complex materials is a major goal of modern pyrolysis mass spectrometry. Unsupervised methods are necessary since pure reference spectra of components are often unavailable. Recent developments in unsupervised mixture analysis using examples from bacteria, jet fuels, and wood are given. Factor and discriminant analysis on 18 strains of Escherichia coli showed a clear differentiation between K1 and non-K1 antigen strains. Graphical rotation confirmed that the differentiation was based on the K1 antigen colominic acid. Binary and ternary mixtures of jet fuel components were used to numerically extract spectra of pure compound classes present in fuel formulations. Mathematically extracted spectra compared favorably to component spectra, which were not included in the data set. The variance diagram technique gave the same directions of the component axes as target rotation, a supervised technique. Variance diagram methods were applied to single samples of wood by recording mass spectra as a function of temperature, since the three major components of wood pyrolyze at slightly different temperatures. A variance diagram with factor 2 expanded showed clearly the three major wood components: cellulose, hemicellulose, and lignin.

The performance of thermal imaging systems depends on a wide group of parameters that are integrated into the minimum resolvable temperature difference (MRTD) expression. The specific analytic dependence is determined by the system implementation and the design procedure used. This work calculates the performance dependence on detector area and optical aperture size and shape when the field of view and the detector angular subtense are held constant due to design procedure and technological constraints. Analytical models for three cold shield types (ideal, rectangular, and no cold shield situation) are described and used for the derivation of the MRTD expressions. The expression for a rectangular cold shield explicitly shows the dependence on basic parameters in contrast to the usage of a cold shield efficiency parameter that is generally accepted. In addition, an analytic model for crosstalk is described and used. It is shown for systems with negligible crosstalk that regardless of cold shield type the detector with the smallest permissible area will yield the best performance and the smallest system, while for systems with crosstalk the benefits of smaller systems, which are possible with smaller detectors, should be weighed against the MRTD degradation through crosstalk. The influ-ence on the MRTD of optical aperture size for round and square optics is calculated for diffraction-limited optics, taking into account different cold shield types. Conclusions are drawn as to the best optical subsystem, using minimal MRTD criteria, under various constraints. It is shown that when an aperture close to the diffraction limit is used, a big improvement in the high frequency range of the MRTD is achievable by using square optics.

Three instruments used at Hughes Aircraft Company for making laser measurements are described. Two of the three instruments employ the conventional aperture technique for measuring beam divergence and use the aperture spatial location as the geometrical center of the beam. The third instrument measures the beam profile with a diode matrix array, and the laser signal amplitude on each pixel is processed by firmware to determine the centroid, beam divergence, energy, and the angular misalignment relative to the optical line of sight. A comparison between measurements made by the aperture technique and the new diode matrix array system shows the beam divergence values were within one percent. Measurement accuracy considerations made when designing a laser test system are dependent on the dynamic range. The detector array method permits single pulse analysis, multiple pulse averages, and storage of pulse data. It also permits quantitative evaluation of laser pulse-to-pulse parameter changes during the initial laser firing period.

The cycling properties of photothermoplastics based on Staybelite Ester 10 can be improved to several thousands of recording cycles. A chemical purification of as-received Staybelite Ester 10 and the use of relatively thick thermoplastic and photoconductive layers are needed in order to preserve both high diffraction efficiency and good cycling properties. Such devices are especially suited to variable beam steering and optical switching.

We have recently demonstrated a passive, picosecond, Si optical-limiting switch for 1 um radiation. Since this device functions below, at, and above the Si melting threshold, its operating characteristics are determined by a large number of mechanisms including nonlinear transmission, self-diffraction, nonlinear reflection, phase transitions, and resolidification morphologies. Here, we review measurements in which we apply a wide variety of picosecond spectroscopic techniques in order to characterize these optically induced phenomena.

A set of multistage image processing algorithms has been developed to perform change detection in image sequence analysis. These algorithms are tailored to the task of moving target identification (MTI). Conventional differencing algorithms are compared to a new spatial differencing algorithm. Subsequent processing is accomplished with thresholding and a suboptimal implementation of a 2-D matched filter designed for simplicity of calculation. The image processing algorithms are then coupled with a simple tracking/detection algorithm. The resulting combination of processing shows very good performance for detecting targets in simulated mosaic IR images, with a projected probability of false alarm less than one per 1011 frames and a probability of detection for targets within the model approaching unity.

A small dark ring is formed when laser radiation is incident normally on a thin slab of transparent material that has an index of refraction greater than one, a smooth, specularly reflecting front surface, and a white diffusely reflecting substrate. The dark ring, which is located on the substrate, increases in size as the thickness of the transparent medium increases. It is formed when (1) the ratio of transparent medium thickness to diameter and (2) the ratio of laser beam diameter to transparent medium diameter are small. Since the radius of the dark ring is a function of the transparent medium thickness (as well as the index of refraction), the problem is two-dimensional. Experimental data are presented for the backscattered radiation in the normal direction as a function of radial distance from the incident laser beam. A geometric optics development is used to explain (1) the ring formation and (2) the effect of finite-sized detection apertures. Comparisons with the experimental measurements are used to verify the theoretical analysis.

In general the Gaussian intensity distribution of a laser beam is truncated at the pupil of the image-forming system. The more pronounced the truncation effect, the less the energy portion used, and it deteriorates toward zero for a very pronounced beam expansion with almost homogeneous illumination. For an image-forming system the Gaussian intensity distribution of the incident beam may be interpreted as an apodization with a Gaussian amplitude in the pupil. Point image, encircled energy, MTF, and depth of focus can be calculated from the pupil function that is defined in this way. For diffraction-limited lenses it is shown how different pronounced truncations of the incident Gaussian beam will affect these image quality criteria. Applications of this effect occur, for example, in optical data storage technology and in infrared laser applications. The smallest point image is obtained for homogeneous illumination of the pupil, but the beam expansion needed utilizes only a small portion of the total incident energy. The more pronounced the apodization effect in the truncated Gaussian beam, the wider the central core becomes. The encircled energy functions for less pronounced apodizations are similar in the central region to those without apodization. Outside a diameter corresponding to the first dark Airy ring an increase of the apodization effect (which means less pronounced truncation) reduces the fraction of the total energy contained in the outer region of the point image. For a 3X Airy disk diameter almost the total energy is encircled for a Gaussian distribution, whereas only some 90% is encircled for homogeneous illumination. A nontruncated Gaussian beam results in a reduction up to about 0.25 in the MTF values in the higher spatial frequency range. With a nontruncated Gaussian beam a depth of focus some 50% larger is obtained, compared with that for homogeneous illumination.

The design of a camera viewfinder having dual magnification is described. Dual magnification means two modes of operation: (1) the "normal" mode in which the actual filming takes place and (2) the "focus" mode in which critical focusing is carried out. This type of viewfinder is ideally suited to camera systems that have large field formats, making it difficult for the user to view the entire field of view instantaneously yet still focus the image exactly on the film.

For in-line Fraunhofer holography in cylindrical tunnels, two methods are proposed to neutralize the window curvature effects. One is to modify the usually flat outer surfaces of the window into curved surfaces parallel to the original cylindrical direction; the desired outer curvature is determined in this paper. The second method proposes two separate parallel cylindrical lenses (one on each side) for zero net power. The desired lens parameters are determined in terms of the known physical quantities.

There are zoom system applications in which transverse image displacement caused by centering errors can be disturbing. By choosing an optimum reference point (adjustment of reference mark), image displacement is minimized. Formulas are given that permit residual image displacement to be already calculated from the design of thin lenses. Examples show that different types of zoom systems differ markedly in sensitivity to this effect of centering errors.

All focal spot sizes in the paper should be reduced by a factor 1 / n and all peak intensities should be increased by a factor n2, where the appropriate indices n are as follows: