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.

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.

Monochromatic electromagnetic wavelets and the huygens principle.

For the first time, to our knowledge, optical diffraction is shown to be a wavelet transform with the electromagnetic wavelets. We show that the optical wavelets proposed by Onural [Opt. Lett. 18, 846 (1993)] are the Huygens wavelets under a Fresnel approximation, and the electromagnetic wavelets proposed by Kaiser [A Friendly Guide to Wavelets (Birkhauser, Boston, Mass., 1994)] reduce to Hyugens wavelets in the case of a monochromatic field.

Non-Bragg orders in dynamic self-diffraction on thick phase gratings in a photorefractive polymer.

We demonstrate that recording thick holographic phase gratings in photorefractive polymers can lead not only to very efficient Bragg diffraction but also to rather strong diffraction into non-Bragg orders. We show that this effect has features drastically different from those of Raman-Nath diffraction on thin gratings. We compare the experimental results with a model based on the theory of dynamic self-diffraction in a photorefractive medium. Applications of this effect in devices for optical image processing are proposed.

Optical syntactic pattern recognition by fuzzy scoring.

A novel syntactic approach is introduced to treat particular problems in pattern recognition. The procedure is implemented by the use of optical correlation methods for identifying the various primitives that appear in the input pattern, and their importance is determined by fuzzy relational scoring. Robust pattern recognition with tolerance to normal variations is demonstrated, indicating an efficient new approach for optical pattern recognition.

Fractional discrete Fourier transforms.

Direct calculation of fractional Fourier transforms from the expressions derived for their optical implementation is laborious. An extension of the discrete Fourier transform would have only O(N(2)) computational complexity. We define such a system, offer a general way to compute the fractional discrete Fourier transform matrix, and numerically validate the algorithm.

Anisotropic photoconductivity and current deflection induced in Bi(12)SiO(20) crystals by a high-contrast interference pattern.

We have predicted and observed an anisotropic photocurrent induced in the cubic crystal Bi(12)SiO(20) by a high-contrast interference pattern. The transverse current detected when the interference pattern is tilted is caused by deflection of the direct current generated by an external voltage applied to the crystal.

Self-organization of scattering in photorefractive KNbO(3) into a reconfigurable hexagonal spot array.

The scattering cone (~2 degrees ) from an Ar laser beam (514 nm) in photorefractive KNbO(3):Fe has been observed to transform into a reconfigurable hexagonal spot array. This phenomenon can be explained through the creation of laser-induced transmission and reflection grating arrays.

Regular geometries for folded optical modules.

We present three new three-dimensional right-cylindrical folded modular interconnection architectures. To compare these systems among each other and with earlier designs, we introduce several figures of merit. The figures of merit describe such aspects of the system as the compactness, the relative angles of the optical axis to optical elements in the system, and system manufacturability. These figures of merit permit the designer of such an optical system to choose the geometry best suited for a particular application.

Dynamics of hologram recording in DuPont photopolymer.

Several dynamical aspects of the DuPont photopolymer film HRF-150-38 for holographic storage are described. We study temporal aspects of exposure, exposure time, processing situations, and storage effect. The quantities studied are diffraction efficiencies, thickness changes, and Bragg angle. The experimental results are performed with an argon-ion laser at 514.5 nm.

Interferometric atmospheric refractive-index environmental monitor.

Long, open-path, outdoor interferometric measurement of the index of refraction as a function of wavelength (spectral refractivity) requires a number of innovations. These include active compensation for vibration and turbulence. The use of electronic compensation produces an electronic signal that is ideal for extracting data. This allows the appropriate interpretation of those data and the systematic and fast scanning of the spectrum by the use of bandwidths that are intermediate between lasers (narrow bandwidth) and white light (broad bandwidth). An Environmental Interferometer that incorporates these features should be extremely valuable in both pollutant detection and pollutant identification. Spectral refractivity measurements complement the information available from spectral absorption instruments (e.g., a Fourier-transform infrared spectrometer). The Environmental Interferometer currently uses an electronic compensating device with a 1-kHz response time, and therefore rapid spectral scans are feasibe so that it is possible to monitor the time evolution of pollutant events.

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.

Space-filling modular optics.

Repeated folding of the optical axis can be used to design space- and volume-efficient optical systems. We suggest that space-filling curves, such as the Peano and Hilbert curves, offer a useful way of realizing compact modular optics.

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.

Concentrators for focal-plane arrays.

It is generally assumed that lenslet arrays are needed to concentrate image light upon the relatively sparse detector areas in a focal-plane array. These have severe field-of-view difficulties and require considerable space to implement. We show how to manufacture optically parallel arrays of concentrators of controllable size and field of view with photorefractive crystals.

Genetic algorithm for optical pattern recognition.

A genetic algorithm is used to generate binary reference functions for optical pattern recognition and classification. Procedures based on the properties of convex functions can be implemented directly on hybrid electro-optical systems. Computer simulations demonstrate the efficiency of this novel approach.

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.

Role of photon statistics in energy-efficient optical computers.

One of the limiting factors in the operation of highly energy-efficient optical computers is the fluctuation in the rate of photon detection events. Squeezed light technology, which appeared to be a possible way to mitigate this fluctuation, is shown to be of limited utility in this field.