Multiplexing ultrasonic wave fronts by holoraphy.

Easily viewable, three-dimensional images have been produced from information derived from the passage of sound through the head of a living human subject. In this technique a new form of holographic multiplexing is used to construct the three-dimensional image from two-dimensional ultrasonic B-scans taken in many separated planes.

Optical parallel database management system for page oriented holographic memeories.

Current data recall rates from page oriented holographic memories far exceed the ability of electronics toeven read or transmit the data. For database management, we must not only read those data but also query them-computationally, a far more complex task. That task is very severe for electronics. We show here the rudiments of an optical system that can do most of the query operations in parallel in optics, leaving the burden for electronics significantly less. Even here, electronics is the ultimate speed limiter. Nevertheless, we can query data far faster in our optical/electronic system than any purely electronic system.

Finding the shortest path in the shortest time using PCNN's.

A pulse coupled neural network (PCNN) can run mazes nondeterministically (taking all possible paths) with constant time per step. Thus, when a signal emerges, it has taken the shortest path in the shortest time.

Digital control of focal distances.

A method is described whereby the focal distance of a lens can be varied digitally using electrooptics or other means without changing the magnification or spot size. The device is limited to lenses with half-angles less than 15 degrees . Pairs of polarization switches and passive birefringent elements are used. A total of 2(N) equally spaced focal positions can be achieved with N switches. If a total length L of birefringent material (indices of refraction n and n + Delta(n)) is used, the total shift in focal distance can be as high as LDelta(n)/n(2). A ten-stage(1024-position)device falls within the limitations set by material and depth-of-field considerations. The shift in focal distance can be magnified optically to arbitrary distances, but the image or spot size is also magnified in the process.Several practical applications of this device are discussed.

Fuzzy syntactical pattern recognition.

It is possible to use Fourier optical pattern recognition to gather the data needed to make a fuzzy comparison of the description of an ideal object. Such an approach allows for changes in scale, location, and distortion.

Improved relaxation processor for parallel solution of linear algebraic equations.

A bidirection matrix-vector multiplication scheme leads to faster convergence as well as guaranteed convergence in a relaxationp rocessorfo r parallel solutiono f lineara lgebraic equations when used in a bimodal optical computer.

Parallel algorithms and architectures based on pipelined optical buses.

Optical signals have some unique properties, such as unidirectional propagation and precisely predictable path delays in waveguides, which are not shared with their electronic counterparts. By taking advantage of these unique properties, we can use optical interconnections to achieve speed improvements in single-instruction stream, multiple-data streams (SIMD) computations. We first show how optical buses can be utilized advantageously in SIMD architectures to obtain fast solutions to several computational problems, including integer addition, counting and logical XOR, sorting, and fast Fourier transforms. We then present a new implementation of the optical buses to meet the unique requirements in highperformance optical-electronic computing systems. Such an implementation allows the transmission of messages at speeds ideal for optics and, in the meantime, the processing of data at speeds ideal for electronics, dealing successfully with the speed limitation by electronics in optical-electronic computers. The primary effects of this bimodal optical bus are twofold: reduction of fiber lengths and reduction of system latency. Reduced latency is a unique advantage to an optical bimodal bus. Together, these observations make optical-bus-based architectures appear to be a promising approach to SIMD processing.

Applications of optical Boolean matrix operations to graph theory.

The transition from optical numerical matrix algebra to optical Boolean matrix algebra is explored in detail. All important Boolean matrix algebra tasks can be performed optically. Quantitative measurement is replaced by a simple light-or-no-light decision, something optics can do well. The parallelism advantage of optics becomes greater as the matrix size increases. As an illustration of utility, we consider graph theory.

High-efficiency rapidly programmable optical interconnections.

An array of optical Fredkin gates implemented by optically controlled waveguide couplers is shown to constitute a very efficient and versatile optical interconnection network with parallel addressing capabilities. The characteristics of the array are analyzed using linear algebra to indicate interconnect programming procedures. In terms of SNR this network is estimated to be comparable with previously proposed architectures. However, from many other aspects (light transmission efficiency, number of switching elements, speed, and fault tolerance) it has significant advantages.

Optical expert systems.

A general approach to using spatial light modulators in expert systems and in related AI methods is discussed. The information capacity of such system can far exceed the capacity of the spatial light modulator itself.

Deconvolution of multiple images of the same object.

Deconvolution of images of the same object from multiple sensors with different point spread functions as suggested by Berenstein [Proc. IEEE 78, 723 (1990); Stochastic and Neural Methods in Signal Processing, Image Processing, and Computer Vision, S. Chen, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 1569, 35 (1991)], opens new opportunities in solving the image-deconvolution problem, which has challenged researchers for years. We attack this problem in a more realistic formulation than that used by Berenstein; it explicitly takes into account image sensor noise and the necessity for adaptive restoration with estimation of all required signal and noise parameters directly from the observed noisy signals. We show that arbitrary restoration accuracy can be achieved by the appropriate choice of the number of sensor channels and the signal-to-noise ratio in each channel. The results are then extended to the practically important situation when true images in different sensor channels are not identical.

Parameter extraction by holographic filtering.

Holographic matched filter pattern recognition has been plagued by too much sensitivity to such parameters as rotation and scale. We show here how to use that sensitivity to make rapid accurate estimations of those parameters. For the particular case studied, we made signal-magnitude independent measurements of four rotation angles from -15 to +15 degrees using three matched filters at -15, 0, and 15 degrees multiplexed onto a single hologram. This leads to obtaining a worst case accuracy (95% confidence) of 1.0 degrees for intermediate angles. The composite filter allows a search to be made electronically in the output plane, thus avoiding any moving parts, i.e., object or matched filter.

Computer recognition of 2-D patterns using generalized matched filters.

Prior work on generalized matched filters (GMF(s)) was limited to eighty points and a 1-D signal. We show here how to calculate arbitrarily large GMF(s). We then compare GMF(s) with other common pattern recognition filters for one particular image using computer simulation. The GMF appears to offer improvements in terms of smaller within-class variability and greater between-class separation relative to matched filters. In addition, the GMF permits far more accurate location of the object in the input scene than the matched filter.

Feedback methods for optical systolic and engagement matrix processors.

The matching of the feedback circuitry to the optical systolic or engagement processor permits simple pipelining of stationary iterative algorithms as well as on-the-fly scale adjustment similar in effect to floating-point calculation.

A technique for producing wide-angle holographic displays.

A new technique has been devised for recording and reconstructing holograms which can be viewed from a wide range of angles simultaneously by a large number of people. The problems which arise through the use of this technique have been analyzed and the limitations delineated. Satisfactory wide angle, three-dimensional displays have been constructed in the manner described by using absorption holograms. The features of these holographic displays agree qualitatively with the predicted theoretical limitations.

Three-dimensional imager.

A mode-locked laser, a rotating beam splitter, and a streak camera are the primary components of an imager with the ability to record three-dimensional images of remote (up to several kilometers) objects in real time in broad daylight. Immediate and future applications are noted.

Propagation of ultrashort pulses through lenses.

Ordinary optical components may behave in extraordinary ways when illuminated with ultrashort optical pulses. In the cases of lenses, only the flat lenses such as Fresnel lenses, Fresnel zone plates, and holographic lenses display such anomalies. For them, the pulse may be both elongated temporally and spread spatially unless very high focal number lenses are used.

Optical communication at the source bandwidth limit.

The possible limiting components on optical communication bandwidth are the source, the modulator, the propagation medium, and the detector. It is easy to show that the source bandwidth is the fundamental limit. The possibility of source bandwidth limited communication is demonstrated theoretically and experimentally. The basic principles involved are readily extendable to more practical partial approaches to this limit.

Optical parallel Dempster-Shafer calculations.

The Dempster-Shafer formalism allows us to update certainties (both beliefs and plausibilities) by taking into account indications from new knowledge sources. We show here that optical parallel Dempster's rule of combination computation is practical because all operations can be broken up into two which have previously been shown to be ideal for optics: vector outer product formation and spatial remapping. Easily available technologies lead us to a device capable of ~10(5) belief updates per second.

Wave particle duality considerations in optical computing.

The wave particle duality inherent in the propagation of light or particles can be exploited for energy efficient computing leading to energy requirement per calculation below kT. Although several reversible computers with similar characteristics were proposed in the past, only optical implementations can be made with the present technology.