Acousto-optic spectrum analyzers (AOSAs) provide a convenient means of separating wide bandwidth signals into their frequency components. The two commonly implemented AOSA receivers are fast frequency channelizers and integrating spectral radiometers. By modifying the input signal and by providing additional digital post-processing, the AOSA can also perform radiometry, signal autocorrelation, and cross-correlation. The latter function allows a matched filter receiver to be implemented for signals that have time durations much longer than the signal processor. The resulting signal-to-noise (SNR) improvements from the receiver are consistent with the time-bandwidth product of the waveform, rather than the time-bandwidth product of the acousto-optic device. A mathematical foundation of the processor is presented along with specific receiver implementations.

Low probability of intercept (LPI), spread-spectrum signals are becoming commonplace in both communication and radar systems. Cooperative receivers process these signals to provide large gains in the output signal-to-noise ratios (SNRs). Given the low signal power expected during reception and the lack of a priori signal knowledge, intercept receivers have difficulties in providing adequate detection of LPI signals. This detection problem is compounded when high power, narrow-band interference is simultaneously present with the LPI signal. A 512-channel acousto-optic spectrum analyzer is used in conjunction with digital processing to implement an autocorrelation-type receiver with interference rejection. Although difficult to implement in radio frequency (rf) or digital electronics, acousto- optic spectrum analyzers may provide a practical solution with sufficient dynamic range for the intercept application. Implementation and algorithm considerations are provided as well as simulated results. Initial experiments confirm LPI signal detection when the signal is minus 5 dB relative to noise and minus 40 dB relative to multiple narrowband interference sources.

In this paper we describe and investigate different types of acousto-optic (AO) signal processing systems that have been designed and manufactured recently. We demonstrate a real- time rf power-spectrum analyzer (RTSA) operating in the 50 - 100 MHz frequency range with high resolution of 35 kHz. Then we present a microwave power-spectrum analyzer operating in a wide frequency range from to 2 GHz with resolution of 1 MHz. The systems are members of an AO-RTSA family mounted in a 19" rack with compact size and vibration free optical part. The received rf and mw signals are digitized, transferred with high speed interface to then processed by a 486 embedded computer. The system bus and modular setup allows the extension -- or reconfiguration -- of the system with various additional units if necessary for a particular application.

We review the basic operating principles involved in development of a real time hybrid opto-electronic radar processor to form a 2-D range-Doppler image for ISAR applications. An overview description of the physical implementation of the processor developed at PSI is included, along with a discussion of the high level processor control structure required for performing the radar algorithm and system test functions. Finally, we present the results of preliminary testing of the pulse compression processor (PCP) which forms the cornerstone of the optical processing operation. The key capability of the optical correlator to map precise phase shifts via direct control of the radar transmitter carrier IF is demonstrated.

Essex has been involved in quadratic processing research and the design of processors that compute these algorithms for the past 14 years. We are developing a more efficient processor (Labyrinth-II^TM) that has higher dynamic range (greater than 100 dB) and enhanced throughput (approximately 70 times faster). Labyrinth-II^TM is a unique half-rack integration of non-developmental units that provides the compute power to solve complex signal processing tasks with significantly reduced latency. The architecture is a flexible combination of high-speed laser optics and digital technologies that is readily configured by the customer to perform a variety of functions. One or two signals can be input to the processor for linear or quadratic processing. The new processor is much simpler, more compact, and more flexible than predecessors. This paper presents a description of this new workstation accelerator. The functions generated by this processor are the ambiguity function, Wigner-Ville function, and cyclic spectrum. Other functions that can be represented by two signal inputs can also be generated by this accelerator. Some applications include high resolution spectral analysis, radar waveform processing, signal detection and characterization, geolocation using time and frequency differences of arrival, and direction finding using angle of arrival.

In-phase (I) and quadrature (Q) signal processing is required when signal phase information is needed, such as to prevent effects like blind phase in pulsed moving target indicator (MTI) radar. A photonic I-Q processor is proposed and experimentally demonstrated for low frequency (e.g., sub-Hz - 15 MHz), radio frequency (e.g., 107 - 133 MHz) and microwave frequency band (e.g., 800 - 1000 MHz) signal processing. Applications for our I-Q processor include signal processing for sonar, ultrasound, radar, and communication radar receivers.

A computer simulation and experimental results are presented to show that use of a time integrating acousto-optic correlator can enable the detection and high resolution direction finding of very low power spread spectrum signals. The correlator operates on the outputs of two spatially separated receivers and the output ccf (cross correlation function) is windowed before the Fourier transform is taken to generate the 'time domain filtered cross spectral density' (TDFCSD). Detection is achieved by threshold detection within the amplitude of this TDFCSD, while direction finding is achieved by phase slope estimation.

A simple acousto-optic system is described that is capable of demodulating frequency and phase-modulated signals using a bicell photodetector. The performance of the system is modeled showing that, by taking the sum and difference of the outputs from the two bicell elements, it is possible to identify and demodulate a wide range of different types of modulation without any a priori information. Thus the technique is well suited for surveillance receiver and ESM applications. In particular it is shown that BPSK, QPSK, offset keyed QPSK, differential QPSK, continuous phase FSK (including MSK) and ordinary FSK all give unique and easily identifiable signatures. Some preliminary experimental results are presented, which are in good agreement with the modeled results.

Over the past few years, we have been continually upgrading and testing an acousto-optic (AO) multichannel adaptive optical processor, the anti-jamming optical beam-nuller (AJOB), with the ultimate goal of mitigating multipath jamming interference in advanced surveillance applications. Multipath signal considerations are often crucial to successful operation and utilization of adaptive interference cancellation radar hardware. Relative time of arrival and signal strength detection are necessary for accurate placement of the necessary nulls. Presented in this paper are the initial test results and the preliminary test plans for conducting simulated multipath jamming cancellation. Thus, the AJOB represents a potential solution to the problem of multisource multipath jamming interference.

High-frequency structure of reference mask used in conventional acousto-optic matched filter (AOMF) does not allow adjustment of impulse response by simple means. Two schemes overcoming this limitation are considered in the paper. For one of them experimental results are discussed.

Two novel all-optical acousto-optic processor designs are introduced for antenna null steering applications. Both designs use an acousto-optic point modulator and a multi- channel acousto-optic deflector in a unique in-line arrangement to form a write/read two color system. One processor is a forward light flow optical design, while the other is a reversible light flow optical architecture. A write-only acousto-optic multichannel correlator processor design is also introduced using a counter-propagating signal correlator design. This processor also uses a time integrating detector such as a two dimensional charge coupled device or a high dynamic range photorefractive crystal for bias free correlation signal detection.

A new class of acousto-optic device that simultaneously achieves a wide angular aperture, broad bandwidth, and high diffraction efficiency is presented. Parallel tangents and beam steering are used simultaneously, which enhances the product of acceptance angle, bandwidth, and diffraction efficiency to be larger than that of isotropic acousto-optic devices by more than one order of magnitude and to be larger than that of tangentially matched acousto-optic devices by more than four times. A wide-angular-aperture acousto-optic device with a center frequency of 150 MHz and operating at 514.5 nm was optimally designed, fabricated, and its performance measured. The consistency between experiment and theory is excellent. This device can also be used as a high speed and high efficiency modulator without any change in design. This was verified experimentally and risetime of 11.7 ns was obtained. Thus, this device can be optimally used as both a wide-angular-aperture Bragg cell/deflector and a high speed modulator.

GaP with shear acoustic mode in (110) direction is one of the few acousto-optic materials which are practical for the AO devices operating above several GHz frequencies. Low acoustic attenuation, low acoustic non-linearity, and high AO figure of merit of this mode in GaP provides remarkably large time-bandwidth products with small apertures and high enough diffraction efficiencies. In addition, the self- collimating (or low diffraction spreading) orientation of this mode in GaP allows selection of a smaller transducer height to improve further the AO diffraction efficiency and to increase the optical throughput with smaller channel spacing in multi-channel Bragg cells. Acoustic diffraction spreading and attenuation measurement in a shear mode GaP AO device operating at 4.2 GHz are reported here. Negligible acoustic beam diffraction spreading in this device allowed us to deduce accurate attenuation data for the shear mode. We measured 1.88 dB/cm-GHz² or 0.77 dB/microsecond- GHz² acoustic attenuation for this mode.

The increase in information capacity of acousto-optic systems can usually be achieved by increasing the bandwidth (Delta) f of their acousto-optic cells. At the present time, acousto-optic cells can have (Delta) f of 1.2 GHz. During the process of manufacturing a system with maximum possible frequency characteristics, some problems could arise, the main one is the problem of electric power feeding to the top electrode of a piezoelectric transducer. This problem is caused by small dimensions of the top electrode (tens or hundred micrometer). Due to the same reason, the acoustic power density drastically increases in the acousto-optic cells (up to 0.5 - 1.0 kW/cm²), which could produce nonlinear effects in the medium of propagation, and thus considerably restrict the dynamic range of the acousto-optic systems. Moreover, high acoustic power localized in a small volume can result in some thermoacoustic effects and even destroy the acousto-optic material. High electric strength (up to 30 - 50 kV/cm) in the material of the piezoelectric transducer can also be a problem. These problems are very hard to solve, and their solutions usually decrease several parameters of the acousto-optic cell, and in some cases, there are no solutions at all. To some extent, feeding the electric power is similar to the common problems of UHF transistor manufacturing, and such experience can be used, but the other problems are very specific and have nothing common in the modern electronics. That is why new alternate solutions are very important.

The theoretical model of spectral filtration of noncoherent light imaging due to collinear and quasi collinear acousto- optic interaction (AOI) in 3D linear-nonuniform crystals is represented. The analytical solutions of the problem and space-spectral transfer functions are found. The theoretical estimation and numerical simulation of space-spectral selectivity and transformation 2D intensity profile of filtrated imaging are given. It was shown that 3D optical nonuniformity cause 2D spatial dependence of frequency- selective properties of quasicollinear AOI and also 2D nonuniformity of spatial transmission.

The performance of the recently described maximum average correlation height filter is compared to the matched spatial filter. It is shown that the former is better for detecting distorted views of a target in noise, and yields higher probability of detection with lower probability of false alarm.

Complex valued zero and fifteen phase state spatial filters incorporating invariance with respect to rotation and elevation are developed for use in target recognition and discrimination. Correlation results for targets in a bright background are shown when these filters are implemented on a high speed optoelectronic signal processor and compared with digital correlation. Further miliary and commercial applications of this technology are discussed.

Optical computing and signal processing is a growing field of scientific research and now more and more entering into industrial applications. Therefore, fast switching spatial light modulators (SLMs) are needed for displaying and filtering processed information. In this paper we present a transmissive ferroelectric liquid crystal display (FLCD) with high performance which will be operated as an SLM in an optical pattern recognition system using incoherent optical spatial frequency analysis (OSFA). The layout and the manufacturing process of the display have been designed especially for the requirements of SLMs in optical systems. The matrix is consisting of a square matrix of 512 columns by 512 rows with a spatial resolution of 508 dpi. An additional black aperture diaphragm of 1 mm is introduced around the active area in the switching plane of the FLC. The display is passively addressed with a multiplex driving scheme using the intrinsic bistability of the FLC. Each pixel of the display represents a switchable half wave plate, resulting in binary amplitude or phase modulated pictures dependent on the polarizer settings. Using an FLC with a high spontaneous polarization and a high pretilt at the substrate surfaces, we obtain excellent contrast ratios of 100:1 and a very high switching speed based on a row address time of less than 7.5 microseconds allowing frame rates up to 500 pictures/sec.

Optical signal processing systems frequently use Fourier transform techniques for correlation, filtering, etc. In practical applications the complex-valued filters placed in the frequency domain plane are often realized by a liquid crystal spatial light modulator (LCSLM). The requirements for such LCSLMs are very demanding, as they should offer a high resolution, high uniformity, low fluctuation in time and an increased number of grayscales or phase steps. We designed and manufactured an active matrix LCSLM (AMLCSLM) and the appropriate driving system meeting these requirements. The AMLCSLM consists of 480 by 480 pixels, each containing an amorphous silicon thin film transistor (aSi-TFT). Although the pixel size is only 50 by 50 micrometer squared, corresponding to a resolution of 508 dpi, an optical aperture of more than 40 percent is achieved. By the use of a transparent storage capacitor the pixel capacitance was greatly increased, resulting in a reduction of the fluctuation in time. The driving circuitry is capable of driving up to 256 grayscales at a frame rate of 100 Hz in dual scan driving mode. For the row scanning the commonly used rectangular impulse shape was substituted by a shortened trapezoidal impulse. As a result a very good uniformity over the area with an overall phase change error of less than 6 percent is obtained.

Photonic time delay line (PTDL) architectures have been proposed for transmit/receive mode antenna applications. These architectures are based on two dimensional pixelated optical arrays that act as optical polarization switching elements. Such elements can be nematic liquid crystal (NLC) arrays, ferroelectric liquid crystal (FLC) arrays, and magneto-optic arrays. Optical delay lines can be formed using either free space or solid optics propagation, as well as non-polarization maintaining fiber propagation for the case of long time delays. In this paper, various optical array based optical beamformer architectures are presented and compared. These different architectures are based on Thompson polarization beamsplitters, and polarizing cube beamsplitters, for both transmissive and reflective geometries. A novel ternary time delay architecture is also introduced that can give 3^N different time delay settings. In addition, a novel wavelength multiplexing architecture using a single channel dispersive fiber PTDL in cascade with multichannel PTDL is proposed for further hardware size and weight reduction.

A real-time diffraction based optical processed 3-D shape recognition system has been built and demonstrated. The system uses an Ar-ion laser interferometer to project variable spatial frequency structural illumination on 3 dimensional targets which are viewed by a camera. The video data is mixed with a computer generated mask (converted to RS-170 video) and the resulting output video signal is sent to a liquid crystal television (modified to function as a spatial light modulator) which is illuminated by a He-Ne laser. The video mixing process, based on a commercial Chroma-Key circuit, generates an arbitrary moire pattern which is a function of the 3 dimensional shape of the target (indicated by the distorted structured illumination) and of the computer generated mask. As an example, the output pattern could be a 1 dimensional Fresnel zone plate (FZP) when the shape of the object is recognized. In this case, the laser illuminated zone plate produces a bright line focus at the predicted focal distance for the correct target, a reduced intensity line focus for a damaged target, and no output for a totally different target. The result is a mixed video-optical processing system that could be used for real-time quality level sorting or other automated inspection requirements. Other types of diffractive masks are simulated with the goal of increasing the area of target inspection and recognizing and discriminating between different targets with a single mask. Limitations and improvements in the current system are discussed.

Electron optical trapping material (ETOM) has proven to be a viable material for thin film optical memory and is being explored commercially for read/write disk. The characteristics of ETOM are discussed including new measurements at femtosecond speeds. The advantages and disadvantages of ETOM are considered. An example of a hierarchical deflection system is provided that uses mirrors, AO cells and EO cells. The status of research in all-optical switches is reviewed briefly for Kerr, cross phase modulation, TOAD, directional couplers, and semiconductors. An example shows how switches can be used to interleave demultiplex an incoming optical fiber bit stream at greater than 10 Gbps into lower data rate channels for storage using deflectors or moving media.

In this paper, we propose a new angular multiplexing method for storage of the image in BaTiO₃. To perform the angular multiplexing, a SA (simulated annealing) algorithm and a LCTV (liquid crystal television) are used. The SA algorithm is used to design a BPH (binary phase hologram) for reference beam generation, and the LCTV is used to modulate the phase. Reference beam is generated by a Fourier transforming of the phase hologram on the LCTV which is controlled by the computer to record and read images in real time. Recording time of each image is determined by scheduled recording method for uniform diffraction efficiency. Through an optical experiment, we show that four images are recorded and reconstructed by the proposed angular multiplexing method.

Theoretical model of non-stationary process of self- amplification of weak holographic gratings in birefringence photorefractive crystals is submitted at two and one- frequency reading in view of multiwave and vector character of interactions. The analytical solutions of interconnected equations of record and diffraction are found. The effects of the spatial-time transformation of the grating and nonuniformity of the gain and also the dynamics of polarization and selective properties has been studied using numerical simulations at inter-mode and within-mode interaction geometries in optically active cubic crystals.

We report on a reconfigurable optical interconnection approach in which static communication graphs are extracted from high level programs and are mapped onto a two stage optical beam-steered/perfect shuffle interconnect. An array of processing elements (PEs) is partitioned into functional units of equal size that are served by one optical input/output (I/O) port per PE. PEs within a functional unit can use any of the optical I/O ports served by that functional unit. An optical beam-steering mechanism in conjunction with an optical perfect shuffle interconnects the functional units. At the highest level, computer programs are written in the Id dataflow programming language. At the next level, dataflow graphs (communication graphs that represent the natural parallelism in a computation) are automatically extracted from the high-level programs. At the lowest level, the dataflow graphs are mapped onto the optical beam-steered/perfect shuffle interconnect. This mapping step is facilitated by a mechanism that redirects optical beams to that the physical interconnect takes the form of the dataflow graph. An intended application is to create low latency realizations of specialized hardware on-the-fly, such as for rapid prototyping. An advantage of this approach over competing all-electronic or static free-space optical interconnection approaches is that the optical interconnect has low depth (two stages) with low fan-out (typically 1 to 3). In previous work, the behaviors of the mappings are studied for randomly generated dataflow graphs. In the work reported here, the behaviors of the mappings are studied for extracted dataflow graphs. We conclude that this interconnection approach is effective for extracted dataflow graphs, using only a single pass through the network, if the interconnect is augmented with a small crossbar within each functional unit.

A multiplexed symbolic substitution method based on an optical correlator is proposed for an optical parallel addition with redundant binary number. The minimum average correlation energy (MACE) filter, which has very low sidelobes and sharp correlation peaks, is chosen as the optical correlation filter in the recognition phase of symbolic substitution. The sixteen coded input patterns of the redundant binary numbers are classified six groups according to the addition results to minimize the number of recognition filters. To implement the smaller optical system, six recognition/substitution filters are multiplexed in two filter planes with spatial carrier frequencies. Through the computer simulation, it is confirmed that the proposed multiplexed symbolic substitution method is suitable for implementation of the optical parallel adder.

Components selected for use within an analog optical vector matrix processor require much attention to detail throughout the design, in order to obtain a high degree of accuracy for the resultant computed data. By incorporating a linearization look-up table, variable parameters of operation such as crossing a laser diode threshold, rf signal mixer intermodulation, or other non-linear events can be corrected and compensated. This paper addresses the lasing threshold and characteristics of the laser diode elements included with an advanced 64 by 64 channel analog optical vector matrix processor, currently under construction at Photonic Systems Incorporated.

Novel two-dimensional (2-D) optical polarization switching array-based photonic time delay units (PTDUs) have been introduced for phased array antenna and wideband signal processing applications. The use of low loss optical fibers allows remoting of the photonic beamformer, along with providing a compact, lightweight, and low electromagnetic interference (EMI) microwave frequency signal interconnection and distribution method, such as needed for very large aperture wide instantaneous bandwidth phased array antennas/radars. However, there are losses associated with multiple fiber interconnects that limit the maximum number of array channels in these systems. Thus, accurate analysis of such losses is crucial to the design of an optimal photonic fiber-based system. In this paper, we present theoretical design and simulation results on optical fiber array interconnects for our 2-D N bit M channel photonic beamformer for wideband phased array antennas. In addition, we discuss an alignment technique for the large channel count fiber arrays proposed for our beamformer that uses V-grooved silicon wafers. Note that these precise V- groove structures are fabricated via crystallographic perfection of the substrate, accurate alignment of the etch pattern with respect to the crystal planes, and optimized etch conditions. This paper discusses these and other fiber array issues.

We present a holographic implementation of accurate associative memory with only one holographic memory system. In the implementation, the stored and test images are coded by using complementary-encoding method. The recalled complete image is also a coded image that can be decoded with a decoding mask to get an original image or its complement image. The experiment shows that the complementary encoding can efficiently increase the addressing accuracy in a simple way. Instead of the above complementary-encoding method, a scheme that uses complementary area-encoding method is also proposed for the holographic implementation of gray-level image associative memory with accurate addressing.

The application of multiple error-correction codes to optical matrix-vector multipliers (OMVMs) can improve the computational accuracy level of these processors. A binary Bose Ray-Chaudhuri (BCH) code was applied to a simulated mod-2 OMVM. Based on the results obtained from the simulations, the conditions under which the use of such error-correction coding is feasible in OMVMs are discussed.

Time-integrating acousto-optic correlators (TIAOC) provide effective means for spread spectrum signal processing in various applications. Proposed by the authors two- dimensional quadrature radio-frequency TIAOC combines relative simplicity of quadrature channel implementation with extremely wide frequency band limited by the corresponding parameter of the Bragg cells used. When designing signal processors for communication or navigation systems, estimation of radio interference impact on system performance is essential. The paper is concerned with evaluation of dynamic range and sensitivity of the TIAOC mentioned with radio interference taken into account as well as external Gaussian noise. General results obtained are particularized for a simple case of harmonic interference. Such an interference is shown to have negligible effect on dynamic range and sensitivity of the device when interference power is less than that of Gaussian noise.

Holographic data storage in BR (bacteriorhodopsin) films has been investigated. The BR film has a fast response time, with high quantum efficiency, high sensitivity, and high spatial resolution. Because of these properties, BR film is attractive as an optical storage medium. Moreover, due to the high spatial resolution, a multiplexing storage scheme can be applied to store a large amount of data. We have demonstrated the possibility of using a phase-multiplexing technique to store the data in BR films. We also show the possibility of using phase masks for spectrum spreading and encoding.

We have developed laboratory prototypes of nematic and ferroelectric liquid crystal optically addressed spatial light modulators with photosensitive layers based on ZnSe, alpha-SiH, pin alpha-SiH, alpha-SiCH, and pin alpha-SiCH. The SLM performance characteristics measured using standard projection and holographic techniques are presented. The advantages and shortcoming of different SLM design versions are analyzed for the use in the wavefront correction and dynamic hologram recording systems. The examples are given for specific implementation of the SLMs in these systems.

The steady bistable regime in FLC layers was found using FLC compositions with its own (volume) bistability. The grayscale in such a FLC possessing high spontaneous polarization value is demonstrated and explained. The row addressing time 50 mks and multiplexivity 1200 (at optical contrast more than 20:1) are reached in FLC passive addressed matrix. Monostable FLC with 2.5 mks response time (at optical contrast not less than 50:1) can be used in fast optical light valves and active addressed matrices for SLM- spatial filters.