In this paper it is shown that the reference beam for true time delay operation of a heterodyne system must be carefully chosen to achieve proper signal time delay behavior. True time delay is defined here as an equivalent delay of the envelope and carrier frequency of a carrier-modulated waveform, resulting in no apparent phase shift of the envelope. For acousto-optic (AO) tapped delay lines, or more complex AO systems utilized for tapped delay line filters, signal excisors, or beamformers, the reference beam must be equivalent to the undiffracted beam exiting the AO device in order to achieve true time delay. Two examples are used to demonstrate the application of the time delay concepts described in the paper. The first example is a heterodyne transform architecture that uses an external reference beam to select a tap position within an AO cell. The second example is an AO tapped delay line filter that employs the undiffracted beam from the AO interaction as the reference beam.

This paper documents the design and characterization of a 54-microsecond(s) , continuously variable, acousto-optic delay line developed for radar testing applications. The operating principles of this new common-path delay line architecture are reviewed, and key component selection issues are discussed. Ultimately, the characteristics of these key components limit the achievable performance of the completed delay line. For example, the laser diode introduces high frequency noise at the output of the delay line. This noise, which is a direct function of the relative intensity noise of the laser, is the limit to the output noise floor. Bragg cell design is presented with emphasis on the minimization of multiple time-delayed signals caused by acoustic reflections. A computer design and analysis tool is introduced that predicts delay line performance in terms of bandwidth, insertion loss, and acoustic attenuation for this slow shear, tellurium dioxide (TeO₂) based delay line. Experimental results are presented showing 10-MHz operating bandwidth at a 33-MHz center frequency. The 3-dB bandwidth is maintained over delays ranging from 0.75 to 54 microsecond(s) .

A dynamic optical system for producing variable delays of a radio frequency signal is presented. The approach uses a micro-laser diode array to tap an acousto-optic (AO) cell at varying spatial positions along the acoustic channel to generate multiple delayed versions of the input signal to the AO cell. The diffracted and undiffracted laser light exiting the AO cell are heterodyne detected at a photodiode. The resulting output signal is maintained at the input signal frequency, but with a delay corresponding to the tap position along the AO delay line. The use of the laser diode array allows for a programmable time delay, programmable weighting of each delay, a large number of delays equal to the number of elements in the diode array, and multiple delays at one time. Experimental results are presented for a two-tap proof of concept system and a sixteen-tap programmable delay line. Results include dynamic range measurements of the input RF power and the input laser power for the system. Areas of application for this device include use as a programmable transversal filter for clutter cancellation in radar, false signal generation in electronic warfare, and coded waveform generation in communication systems.

This paper presents descriptions of and results from two quadratic processing workstation accelerators. One of these workstations is used for radar processing and the other two for signal detection and characterization. These workstations exhibit high dynamic range and real-time performance in compact packages. The functions generated by these systems are the ambiguity function, Wigner-Ville function, and cyclic spectrum. Two of these systems are complete and the other is under development.

In this paper we describe and investigate an acoustooptic system capable for detecting and simultaneously determining both the frequencies and directions of several RF sources with short transmission time. Test measurements of the system have been carried out both in laboratory and real environment. Correction of aberrations of the optical system, correction of the frequency- phase difference characteristics of the antenna array, digital filtering of the output intensity distribution, spurious signal suppression, distinguishing CW and hopping signals; and improving the hopping signal resolution using histograms have been demonstrated. High angular resolution of 1 - 2 degree(s) and frequency accuracy of < 100 kHz for both CW and hopping signals in a relatively broad frequency range have been achieved.

This paper reports on the system concept, design and hardware analysis of a wideband transmultiplexer implemented with acousto-optic technology. The objective of the study was to determine the feasibility of constructing a unit that would convert a 20 MHz analog IF band of 5000 contiguous frequency multiplexed 4 kHz channels to a time division multiplexed format. The principal advantage sought over purely digital technology is small size and low power.

We built and experimentally tested an in-line interferometric time integrating correlator. This design demonstrates performance improvements compared to other time integrating correlators, because the +1 diffracted orders, which carry the information to be correlated, travel over a common path and because the undiffracted light from the first acousto-optic (AO) cell is used as the input to the second AO cell. The architecture also provides control of the correlation spatial frequency to match the detector elements spatial frequency. The simplicity of the design, improved light efficiency, and increased optical stability make it an attractive alternative for applications in radar signal processing and spectrum analysis.

We present the architectural and functional details involved in the development of a hybrid optical/digital processor for use in High Resolution Radar applications. Specifically, we describe within the context of a general radar receiver, the use of an advanced analog (optical) front end to perform the computationally intensive correlation processing required for range compression, while providing a requisite set of baseband data containing a phase history of the targets motion to be subsequently doppler filtered digitally in a separate post processing step.

Processing of spatial and temporal optical flows with real time local correlation technique is described and discussed. Simulations and experiments with a time integrating acousto-optical correlator on real stereoimages are reported together with simulation on particle image velocimetry processing. Local correlation of 2D images done with an 1D correlator is here demonstrated by using projection in the 2D image.

A new design for a wide angular aperture Lithium Niobate acousto-optic Bragg cell is proposed. Parallel tangents, beam steering, and an acousto-optic interaction in a rotated 60 degree(s)-YZ plane are used simultaneously, which enhances the product of acceptance angle, bandwidth, and diffraction efficiency to be larger than that of isotropic acousto-optic Bragg cells by more than one order of magnitude. The analysis and optimum design procedure for acoustic beam steering in birefringent acousto-optic diffraction with the parallel tangents condition fulfilled is established and is essential for obtaining the maximum value of the above mentioned product. The acousto-optic interaction in the rotated YZ plane is analyzed and is important to obtain high diffraction efficiency for most cases where the parallel tangents condition is used. The optimal design of a wide angular aperture Lithium Niobate device working at 514.5 nm and with a center frequency of 150 MHz is carried out and is being fabricated.

Optical heterodyne detection requires frequency shift of an optical beam, which can be realized using an acousto-optic modulator (AOM) that shifts the frequency of the diffracted beam with the acoustic frequency (from several tens of MHz, typically). Low frequency shift can be achieved using two, consecutively placed, modulators driven with slightly different frequencies. This configuration, however, results in lower efficiency and higher complexity. To avoid these problems and extremely low frequency, TeO₂ based, single cell AOM have been developed. The AOM performance has carefully been investigated and design considerations maintaining the high diffraction efficiency are given. The suppression of the unwanted effects arisen from low frequency operation, such as presence of multiple diffraction orders, elliptical distortion of the diffracted beam, has been examined. The special anisotropic diffraction geometry allows a frequency shift as low as 5 MHz with diffraction efficiency greater than 85% (> 90% at 8 MHz), simultaneously, as it has been demonstrated.

The effect of laser noise on the frequency resolution of an acousto-optic FM demodulator is investigated. Formulae are developed which allow prediction of the demodulator's frequency resolution when affected by laser intensity noise. The limiting laser intensity SNR is calculated in order to determine the required laser SNR which will not degrade system performance.

A polychromatic acousto-optic modulator was used as a wavelength selector in an argon ion laser. It was mounted inside an argon ion laser mirror holder. The characteristics of the laser with and without wavelength selector were measured and are reported here. The single line output intensities of laser with the polychromatic acousto-optic modulator and an intercavity Brewster prism wavelength selector were compared to estimate the effect of gain competition among lines.

The systolic algorithm approach is currently the most effective design procedure for minimizing computing time and the number of processors. In this study, a method is proposed for designing systolic arrays for arbitrarily large LMS filters. The development process involves the design of the (1) computational graph, (2) computational scheme, (3) interconnection scheme, (4) proposed processing element, for computing the output, y_j at time j, and PE_k protocol. The protocol controls input data flow properly and efficiently. This control ensures that values of input variables are not overwritten during their computing, while achieving maximum parallelism and thus reducing waiting time.

In this paper, a spiral systolic array (SA) architecture with asynchronous controls for the real time realization of an N point DFT and IDFT is considered. The study includes the overall system block diagram, propagation of data between array PEs, operations within each PE, and the PE protocol for computing an N point DFT. The idea is to design self-timed processors and communication protocols to gain control of data streams such that each computation can start if all its data are available, thus reducing waste time. The PE protocol controls input data flow properly and efficiently. The proposed SA has large throughput at the expense of more hardware than FFTs.

A spatial statistics of speckle is changed strongly after field binarization. The same is true for temporal statistics of dynamic speckle. In the study the probability density function of the speckle number if investigated experimentally for binarized dynamic laser speckle field. The dependence of probability density function from threshold of intensity crossing is studied too.

Three different acoustooptical (AO) processors for radio-astronomy are described: AO spectrum analyzers, AO image processing system for solar observations and AO dispersion compensator for pulsars observations. Their principles of operation and peculiarities are described. Characteristics of developed setups, results of their laboratory investigations and also their usage on Russian radiotelescopes are given.

In this talk, based on the key operations governing all these matrix-matrix multipliers, we propose a statistical model to quantitatively analyze the numerical accuracy that these multipliers could deliver. Our study indicates that no matter what particular scheme is used, statistically the numerical accuracy limit caused by the use of analog computation mechanism is much more serious than the dynamic range and other limits to a matrix-matrix multiplier. Our study also shows that when these multipliers are used for, instead of generating algebraic results, the single threshold operations, such as the operations required to implement a programmable logic array, a content- addressable memory, and a neural network, a better accuracy can be expected depending on the used threshold positions.

We describe the architecture and packaging of the flexible detection and postprocessing system.

An adaptive optical radial basis function classifier for handwritten digit recognition is experimentally demonstrated. We describe a spatially- multiplexed system incorporating on-line adaptation of weights and basis function widths to provide robustness to optical system imperfections and system noise. The optical system computes the Euclidean distances between a 100-dimensional input and 198 stored reference patterns in parallel using dual vector-matrix multipliers. For this experimental software is used to perform the on-line learning of the weights and basis function widths. An experimental recognition rate of 86.7% correct out of 300 testing samples is achieved with the adaptive training versus 52.3% correct for non-adaptive training. The experimental results from the optical system are compared with data from a computer model of the system in order to identify noise sources and indicate possible improvements for system performance.

In this paper, we extend our earlier work in image algebra (IA)-based optical processing to the optical computation of high-level image operations (HLIOs) such as connected component labelling, determining component adjacency graphs, finding corresponding points in stereo pair images, and computing the Euler number. In particular, we transform an IA expression that describes a given image procedure into the dataflow graph of the corresponding MEA-conformable (Multiple Execution Array) architecture. From the MEA dataflow graph, we deduce the components and connectivity of a corresponding optical processor. Analyses emphasize computational cost inclusive of propagation time, as well as information loss expected from optical devices such as Spatial Light Modulators.

In this paper, the design and implementation of a high speed optical ring topology based free space optical interconnect is described. This interconnect system operates at 500 MHz and consists of 16 laser transmitters, a four channel free space interconnect, and a fast speed receiver. A Nearest Neighbor interconnect has been successfully demonstrated. At the data rate of 500 MHz, the total system throughput is 8 Gbps. The system can easily be operated at much higher data rates since the rate was only limited by the electronic circuitry. A discussion is given about device issues such as optical switching devices and practical system design issues such as integration and interface with current electronic systems is considered. This interconnect is very promising in the implementation of ultra fast massively parallel SIMD machines.

Using what is available to free-space optics, it is possible to construct a 4D network which multiplexes the time, temporal frequency, space and spatial frequency channels so that the switching complexity is reduced from the order of N² to the order of N^5/4. We proposed and experimentally demonstrated a simplified version of this network based on some multichannel acousto-optic deflector arrays.

This paper reviews two demonstration hardware devices built to show the advantages and potential of holographic optical interconnect techniques for use in a 3D optoelectronic computer architecture.

2D monolithic grating spectrometers for dense wavelength division multiplexing (WDM) show considerable promise to extend the usable bandwidth of optical fibers. Their performance is fundamentally dictated by the grating which is used. First order gratings will theoretically improve the performance of monolithic WDM devices, since WDM devices based on first order gratings do not suffer from an inherent tradeoff between efficiency and broadband operation.

3D superposed holograms of co-orthogonal wave fields are investigated. Two operations were performed when using these holograms. One of them presents the expansion of the wave field of the object in set Walsh functions. The mentioned hologram was also used for switching of optical channels. The objects were presented by a set of 7 luminous points having different phases. Wave fields of the objects were expanded in a set of 8 Walsh functions. Complex amplitudes of the object waves were calculated from the measured coefficients of expansion. The switching of one input optical channel to 8 output channels was accomplished by phase modulation of incoming wave corresponding to Walsh functions values.

New optical implementations of single and multichannel symbolic substitution systems are proposed. The systems are fully programmable, can be used with large patterns and are capable of processing large input images at relatively high speeds. Configuration and structure for a variety of morphological transformations such as erosion, dilation, opening, closing and skeletonization are detailed. Simulation results are presented.

Over the last four years, Essex Corporation has been developing an image reconstruction system (ImSyn^TM) for a variety of applications, including synthetic aperture radar, magnetic resonance imaging, and other sensors. Each of these formats encompasses its own set of requirements for image quality, image size, and throughput. The ImSyn system has been designed to provide image dynamic range of up to 100 dB, arbitrary image sizes, and throughputs of 30 images per second to satisfy the various requirements. Recent efforts to enhance the ImSyn breadboard version has required the development of modeling techniques to measure system performance and identify sources of error and artifacts. The modeling approach, application of the measurements to determine and improve system performance, and the resulting imagery achieved with the ImSyn breadboard are presented.

We demonstrate in the laboratory the construction and correlation of a matched filter correlator using only a single curved element. Previously we demonstrated a correlator that uses a converging reference beam for constructing a matched filter so that when performing correlation, the correlator does not require a lens for taking the inverse Fourier transform. This paper demonstrates an extension in which we use a diverging beam from a laser diode for constructing the hologram in order to avoid a lens for generating a converging beam. The matched filter is turned upside down and reversed for use in the correlator.

In this paper several systematic and random filter plane errors are related through a single parameter that describes the amount of phase mismatch. A model of peak-to-noise ratio (PNR) is also presented that describes the combined effects of random and systematic errors. This expression contains the products of two functions, one that depends only on systematic, the other on random, phase mismatch. PNR is also a function of the number of pixels in the filter plane modulator and a normalized moment the amplitude of the image spectrum. The model is useful for developing phase error budgets for correlation systems.

Twisted-nematic liquid crystal televisions (LCTVs) are currently widely used as spatial light modulators in coherent optical processing systems. With such devices, `phase-' or `intensity-only' modulation is not easily achieved. In this paper we present procedures for finding some specific operating modes that can be achieved with these commercial LCTVs. The operating modes were found both by studying the Lu and Saleh model of LCTVs, and by referring to previous laboratory measurements. We will introduce a simple experimental procedure that can be used to locate a phase-mostly operating mode. The operating modes are considered in the context of a coherent optical correlator.

This paper is a report on the characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of Miniature Ruggedized Optical Correlators for Optical Pattern Recognition. Pixel size is under one mil center to center, one-third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems.

In this paper , a binary joint transform correlator (BJTC) based on an electronically-addressed spatial light modulator is described. The system mainly includes a cathode-ray-tube coupled liquid crystal light valve (CRT —LCLV) , a CCD camera , and a microcomputer. On the base of theoretical analysis ,results of digital simulation and initial experiments are presented , and show that the correlator has good discrimination.

A novel all-optic waveguide crossbar switch based on an in-house developed birefringent material is presented here. This switch uses visible light ((lambda) equals 514 nm) for programmable beam addressing to provide all-optic reconfiguration in both single-mode and multi-mode waveguides. An array of waveguide beams can be addressed within milliseconds using very moderate optical pumping powers (below 100 (mu) W). This allows green emitting diodes to be used for signal switching. The switch is characterized by high speed, high switching sensitivity, low waveguide loss, low optical noise levels, erasability, and reasonable cost.