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A phase-encoded object has been modeled as the input to a joint transform correlator. The joint transform power spectrum is modeled as a binary phase object to calculate the correlation output. The results have been experimentally verified using a liquid-crystal television operating in the phase modulation mode.

The recent production of a deformable mirror device (DMD) spatial light modulator has naturally led to techniques of using this device in popular optical correlator architectures. In this paper, the DMD is used in both joint transform and VanderLugt arrangements. In some cases, the DMD is used as the input device to a single stage joint transform correlator, and in other cases it is used as the filter device in a VanderLugt correlator. A liquid crystal TV is also used for real time addressing of filters displayed on the DMD.

Non linearite observee en utilisant un correlateur optique de Vanderlugt etalon comme poursuiveur de corps mobile

The benefits of stereo vision are numerous and quickly become apparent when attempting to perform simple tasks without the aid of stereo cues. The proliferation of remotely operated vehicles and indirect viewing applications has resulted in an increased need to see the operational environment in stereo. Several approaches to the display of stereo imagery have been demonstrated. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays require no headgear but typically have tight limitations on the position of the viewer's head. Previous papers have described a new type of stereoscopic display based on dual liquid crystal displays. The new display provides a stereo view without temporal or spatial multiplexing. Several prototype displays have been built and demonstrated to potential users with favorable reviews. With a successful proof-of-principle prototype completed, the effort is focusing on improvements to the image quality, consolidating the electronics, and packaging the display for use in rugged environments. The results of this effort should produce a rugged, compact, multiuse stereo display.

The dome or window on a sensor suite seems, at first glance, to be a relatively low tech item. In reality, it can be one of the most costly items in the system. The choice of materials is highly dependent on the sensor, the anticipated operating conditions, and other requirements such as electromagnetic interference or radar cross section issues. The situation is further complicated when multiple sensor bands are used. Some dome materials are suitable for visible or near infrared applications, some for midwave infrared applications, and others for long wave infrared applications. Materials are also available which can be used for dual band sensors such as visible and midwave sensors. The Army is currently developing a tri-mode seeker containing semi-active laser, midwave infrared, and millimeter sensors all using a common aperture. This added complexity is nowhere more apparent than in the missile dome. Optically transparent infrared optical materials tend to have relatively high dielectric constants. Millimeter wave radomes typically have low dielectric constants. Electromagnetic shielding for an optical seeker frequently consists of some type of grid that serves as a wideband filter. Electromagnetic shielding for millimeter wave missiles may use complicated frequency selective surfaces that block all but the frequency of interest. Unfortunately, those frequency selective surfaces tend to be predominantly metal and are opaque in the optical regime. This paper will discuss the unique requirements that are placed on a tri-mode seeker as well as efforts to meet those requirements.

New military requirements have reinvigorated the need for transparent magnesium aluminate (MgAl2O4) spinel. Surmet has developed a process that yields high quality transparent spinel at production scale. Several issues related to the extreme requirements of processing ultrafine spinel powders are described. Transmission data is presented for a significant dataset of parts made by this process. More recently, the process has been expanded to include a capability for producing domes for the Joint Common Missile program. Domes at nominal 6” and 7” diameter have been successfully fabricated. Despite early challenges related to the forming portion of the process, a repeatable capability for these domes has been demonstrated. Several challenges remain in spinel processing in order to support additional military requirements. In particular, the strength of the material needs further improvement. Also, improvements in optical quality with regard to inclusions are needed.

The proliferation of remotely operated vehicles (ROVs) has resulted in a need for the capability to see the operational environment in stereo. In a previous paper the theoretical underpinnings for new types of stereoscopic and autostereoscopic flat-panel displays with full-time, full-resolution images (i.e., no temporal multiplexing and no spatial multiplexing) were presented. Recently, a stereoscopic prototype has been constructed at the U.S. Army Aviation & Missile RDEC and testing is underway. The research presented here describes the application of two liquid crystal displays (LCD) sandwiched together to form a compact, rugged stereoscopic display. Polarized glasses are used to view the image in stereo. The prototype provides a full-time, full-resolution stereoscopic 3D display in a package slightly thicker, but no larger, than the standard liquid crystal display used in laptop computers. The LCDs have been characterized using a Stokes vector polarimeter. The characterization results were very interesting and led to some changes in the encoding algorithms. Significant improvements in the display quality were achieved through these adaptations.

Stereo imagery has been a goal in optics research since the invention of the stereoscope in 1834. While the market has been inundated with displays of various types, sizes, and formats, no general purpose, easy to use, inexpensive method for the display of imagery in stereo has been developed. The benefits of stereo vision are numerous and quickly become apparent when attempting to perform simple tasks without the aid of stereo cues. The proliferation of remotely operated vehicles and indirect view applications has resulted in an increased need to see the operational environment in stereo. Numerous approaches to the display of stereo imagery have been demonstrated. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays, so named because they do not require the headgear, typically have tight limitations on the position of the viewer’s head. Previous papers have described the theoretical underpinnings for new type of stereoscopic displayed based on dual liquid crystal displays. The new display provides a stereo view without temporal or spatial multiplexing. This paper will present the results from experiments to characterize the display components and the resulting changes in the encoding algorithm.

Stereo imagery has been a goal in optics research since the invention of the stereoscope in 1834. While the market has been inundated with displays of various types, sizes, and formats, no general purpose, easy to use, inexpensive method for the display of imagery in stereo has been developed. The benefits of stereo vision are numerous and quickly become apparent when attempting to perform simple tasks without the aid of stereo cues. Numerous approaches to the display of stereo imagery have been demonstrated. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays, so named because they do not require the headgear, typically have tight limitations on the position of the viewer's head. The research proposed here will investigate the application of two readily available, inexpensive liquid crystal panels sandwiched together to form a compact, rugged stereoscopic display. The appropriate drive signals are provided to the two stacked panels, which encode in polarization, the left and right images. Standard polarized 3D glasses can then be used to view the image in stereo. The proposed display will provide stereo pairs without loss of resolution or frame rate and without strict limitations on the placement of the viewer’s head.

A stereoscopic or autostereoscopic display based on this technology provides full resolution and freedom of movement, but with no flicker. Simply put, the display is neither spatially nor temporally multiplexed. It sounds unbelievable, but it's true -- an autostereoscopic display where each eye sees every displayable pixel on the screen at all times. This technology is designed for flat-panel displays, such as LCDs and has the following characteristics: (1) The display is not spatially multiplexed. Each eye sees the full native resolution of the entire screen. (2) The display is not temporally multiplexed. The image for each eye is visible continuously, i.e., at all times. (3) In its simplest form, this technology provides a full-time, full-resolution stereoscopic display for multiple viewers wearing passive polarizing glasses. (4) A variation of this technology can be used to make a full-time, full-resolution stereoscopic projection system for viewers wearing passive polarizing glasses using just a single projector. (5) With the addition of a dynamic aiming mechanism, and an adjustment in the display's output, we can create a single-user, full-time, full-resolution autostereoscopic display requiring no glasses and providing full freedom of movement. Software applications can use the same information about viewwer position to provide natural, full "look-around." (6) A hybrid version of the display can alternate between autostereoscopic (single-user, no glasses) and stereoscopic modes (multi-user, passive glasses).

Optical correlators using spatial light modulators in the filter plane have been discussed and presented for many years. In most cases, these devices are electrically addressed modulators and the filters are generated off-line in software. These filters can be tailored to fit the desired application but cannot be adjusted to account for real-time changes in the target appearance. In addition, building filters to account for all of the possible viewing configurations can strain the reference database and the memory storage capability of the system. Recently, a correlator architecture that used an optically addressed, multiple quantum well (MQW) spatial light modulator as the filter plane device was presented. The architecture is a modified Vander Lugt correlator with and additional input modulator. The filter formed by the interference of the reference image beam and the reference beam is recorded on the MQW spatial light modulator. The recorded filter retains the full complex information as high-resolution film did years ago. Additionally, the filter can be updated simply by changing the pattern on the reference input modulator. The second input modulator is used to address this stored filter in a normal correlator read-out configuration. The correlator has been completed and results will be presented as part of this paper.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pulse couple neural networks (PCNN) have demonstrated some very desirable properties. Chief among these is its ability to segment images very rapidly and very well. This capability has been demonstrated with many different types of imagery including synthetic aperture radar imagery, infrared imagery, optical correlator output imagery, and medical diagnostic imagery. Most of the implementations of this network have been done in software. Several attempts have been made to build electronic versions with varying degrees of success. Recently, an Army Phase II SBIR was awarded to incorporate a PCNN in a smart detector for both military and medical applications. One of the inherent difficulties in building an electronic PCNN is implementing the linking field that is the strength of this network. An optical implementation of the linking would potentially simplify the problem and take advantage of the inherent parallelism of optics. The resultant hardware could be simpler and faster than previous implementations making it an attractive solution. This paper will discuss the current status of the SBIR program, and present possible optical implementations using recently developed Vertical Cavity Surface Emitting Laser arrays.

Digital image interpretation is the basis of medical diagnoses. Through extensive review of patient data, an algorithm was developed to identify features of diagnostic importance in radiological images. The algorithm is generally applicable. Results from cardiac, lung, and military imagery are reported. The algorithm uses a pulse coupled neural network. It is this neural network that is fabricated on a custom CMOS chip. Each neuron of the pulse coupled neural network accepts an external optical input. The optical input is accomplished by a photo-detector. The neurons communicate laterally through a voltage grid. The communication strength, light sensitivity and other global parameters are under external control. A programmable logic array is on the camera board. Data for a specific neuron is accessed by an addressing scheme typically used for a CCD array. The individual neuron speed ranges from 10 to 50 Mhertz, and is fixed by a digital clock. The current chip is configured to operate at 300 Hertz. The chip logic is a hybrid of analog and digital circuitry to minimize the neuron size, maximize the number of neurons at a fixed cost. The hybrid circuitry also minimized the noise level in the chip.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A vanderLugt correlator is under construction using two Sanders binary Multiple Quantum Well Spatial Light Modulators. This correlation is part of the U.S. Army Aviation and Missile Command's three-year program to evaluate the latest generation hardware available for image processing. The Sanders modulators offer extremely high frame rates that make them attractive for image processing applications. The limiting factor in this correlator will actually be the output detector rather than the spatial light modulator. The correlator will be evaluated using infrared imagery to determine its performance in a target cueing/target screening applications. The results from these experiments as well as future plans will be presented.

Poor performance in key components has limited the development of optical target recognition systems. New components are now available, however, that exhibit size and speed characteristics compatible with image processing applications. The U.S. Army Aviation and Missile Command is well known for acquiring and testing a variety of spatial light modulators for image processing applications. We have recently acquired a pair of Sanders Multiple Quantum Well Spatial Light Modulators. These modulators will be evaluated in a manner similar to that used with previous modulators to determine contrast ratio, switching characteristics, optical efficiency, and residual phase modulation. The results of these measurements will be presented.

Poor performance in key components has limited the development of optical target recognition systems. New components are now available, however, that exhibit size and speed characteristics compatible with image processing applications. The U.S. Army Aviation & Missile Command has recently begun a program to exploit the new devices for both homing and imagery analysis applications. New architectures and algorithms which exploit the modulation characteristics of the new devices are being developed and tested. Part of the program is also aimed at funding improvements in the devices to better meet the requirements for optical target recognition. This paper will discuss the overall program, specific devices under consideration, and present the architectures and algorithms under development. Any experimental results available at the time will also be presented, with more detailed results to be presented at a later conference.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We review GaAs Fabry-Perot vertical cavity multiple quantum well (MQW) spatial light modulators (SLMs) developed at Sanders, a Lockheed Martin Company, and demonstrate their use in optical image correlation. These MQW SLMs are reflective- mode modulators using electrically-tunable absorption to modulate the reflected intensity. The operation of the MQW SLMs with a newly-developed Labview graphical user interface is described. A compact Vander-Lugt image correlator is described which was configured using MQW SLMs: binary 128 X 128 pixel image input with a binary filter plane. In addition, the architecture of 8-bit gray-scale MQW-SLM module developed at Sanders is discussed. The performance of the image correlator was characterized using amplitude-encoded binary phase-only filters and various test targets including test imagery supplied by US Army AMCOM, and is compared with simulations for peak-to-secondary efficiencies on these data. Finally, high-speed (250,000 frames per second) target recognition of 128 X 128 pixels binary input imagery is demonstrated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A 32-channel system has been designed and built to process large-format synthetic aperture radar imagery. Eight Vander Lugt optical correlators operate in parallel, controlled by a single-board VME computer. The full-size images are divided into subscenes to match the processors' SLMs and compared to a stored filter bank. Each correlator incorporates two LCDs, four diffractive optical elements, a large CCD sensor, and a DSP based neural network post- processor. Custom drive electronics derive the LCDs at 60 Hz and double their normal operating resolution. The system is self-calibrating and automatically adjusts for a failure in any of the 8 processors. This paper will present a system level overview and discussion of each of the major sub- systems.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Composite filters offer one solution to the problem of scanning numerous filters to find a single target at any aspect, orientation, or configuration. Many different techniques for generating composite filters exist, each with their own advantages and disadvantages. Liquid crystal televisions are an increasingly popular choice for spatial light modulators and are characterized by a coupled phase and amplitude response. The coupled response can cause a problem if not accounted for, however, it can also be used to more closely approximate the desired filter response. This paper will present the results of using optimally encoded composite filters on a LCTV for optical pattern recognition applications.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Automatic target recognition has a wide range of applications spanning many different imagery formats. These input formats include, but are not limited to video, infrared imagery, and synthetic aperture radar imagery. Optical correlators, while not the total ATR solution, have the potential to aid in this complex task. One area of recent interest has been near and far field effects in synthetic aperture radar imagery. An optical correlator has been used to qualitatively assess the differences in imagery obtained for both the near and far field cases. Reference filters were made for each case and compared to imagery from the opposite case. The results of these experiments will be presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In 1986, the U.S. Army Missile Command (MICOM) unveiled the world's smallest optical correlator to demonstrate the ability to make small rugged optical processors capable of surviving transportation and use outside the laboratory. That capability has now been extended. A new solid block correlator has been built for MICOM by the Optical Corporation of America Applied Optics Division. This advanced solid block correlator (ASBC) is based on the same designed used for the original solid block correlator, but incorporates liquid crystal televisions in both the input and filter planes. The ASBC also has the advantage of two separate filter channels to increase filter throughput or allow simultaneous monitoring to the response to two different filters. This paper will present the results obtained from evaluation tests performed with the ASBC.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new solid block correlator has been built for the U.S. Army Missile Command by OCA Applied Optics. This Advanced Solid Block Correlator (ASBC) is based on the same design approach useful for the original solid block correlator. The ASBC provides both improved performance and a vehicle for evaluating the recently available Liquid Crystal Televisions as spatial light modulators (SLMs). Performance is significantly enhanced by: (1) real-time programmable filter capability, (2) improved SLM speed, and (3) improved SLM uniformity. Furthermore, the ASBC also has the advantage of two separate filter channels to increase filter throughput or allow simultaneous monitoring of the response to two different filters. This paper will present the results obtained from initial tests performed with the ASBC.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Weapons Sciences Directorate of the U.S. Army Missile Command has been directly involved in research and development of optical processing technology for several years. Extensive publications have described developments in several key areas of research. Current efforts are aimed toward military applications, for which optical processing offers great potential for improved speed and performance in automatic target detection, location, and recognition. Research is directed toward overcoming the remaining technical issues. Topics of investigation include: spatial light modulator performance and use; photorefractive materials for data storage; Vander Lugt, joint transform, and acousto-optic correlator designs; neural network implementations for morphological transforms, region and texture segmentation, rapid training techniques; and composite filter design, development, and implementation. This paper describes progress and accomplishments in some of these areas, with projections for future work.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The off-axis joint transform correlator improves on the extant on-axis jo transform correlator by eliminating the requirement for a second laser frequency and the means for blocking the first laser frequency from propagating beyond a given point in the correlator. These eliminations are accomplished by using a beamsplitter and a mirror to bring a second portion of the first frequency at an angle to read the pattern information written onto a spatial light modulator by the first portion.

Liquid crystal televisions have become increasingly popular as low cost spatial light modulators. While the early devices suffered from poor resolution and low contrast, recent models compare favorably to the more traditional (and expensive) modulators. Most of the LCTVs are addressed through an RF interface to the external antenna or through a direct video input. This is a convenient interface for an input plane spatial light modulator where the scene information is provided by a video camera. Filters, however, are generally computer generated and the conversion to video can sometimes be an awkward step. A new drive circuit for the Epson Crystal Image video projector is currently under development at the U.S. Army Missile Command which allows pixel level control of the liquid crystal sandwich. This paper will discuss the proposed circuit designed to allow pixel by pixel control of the LCTV.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A simple target which contains a wide variety of spatial frequencies has been developed for use in testing optical correlators. This target is designed to be complicated enough to provide an adequate test of many correlator and filter architectures, but yet simple enough to be used by researchers without the need for special equipment. Computer simulations and experimental results are presented for using the target in testing some correlator filter designs.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical processing systems have been in existence for over 20 years but few have made the transition from the laboratory environment to the commercial environment. Pattern recognition done with optical correlators is one area which is now showing promise for applications outside the laboratory. Many papers have been written in years past on the need for better and faster spatial light modulators and more efficient filtering schemes prior to commercializing an optical correlator. The current state-of-the-art is now approaching this point. Two companies are even marketing Liquid Crystal Television based correlators. The purpose of this review will be to examine the current capabilities of optical correlators and to match those capabilities to existing requirements.

It is generally acknowledged that the performance of an optical correlator is dependent on the input scene contrast. The magnitude of this dependence has yet to be determined, however. As optical correlators begin to move from the laboratory into less benign environments, a better understanding of this effect is required. This presentation will focus on two aspects of the problem. First, given a filter made from a perfect, i.e., high contrast, target, how do changes in the input scene contrast affect the correlation peak to noise ratio? Second, given that the input scene will be low contrast, should the filter be made from a high contrast target or a low contrast target? The results of experiments designed to answer these two questions for a limited number of targets and backgrounds will be given and some general conclusions drawn.

It has been found that binary phase only filters made of real-world scenes are sensitive to changes in the target illumination angle. The illumination angle dependence for several cases will be measured, and a novel technique for reducing this illumination angle sensitivity will be introduced. A filter composed of sections of several filters is used to reduce scene illumination dependence. These filters are made with the target illuminated from different angles, and the resultant filter is more tolerant to changes in target illumination. The filter construction technique as well as results obtained when such a filter is used will be discussed.

Phase-only/binary-phase-only filters have been shown to give sharp correlation peaks in optical correlations. However, these filters transmit all the incoming light, including noise, to the correlation plane so that, theoretically speaking, under additive white noise corruption the signal-to-noise ratio is zero for these filters.1 The optimal phase-only/binary-phase-only filters recently studied1,2 incorporate the use of a supporting binary amplitude function that masks out certain regions of the filter and consequently increases the SNR ratio. While an optimal binary-phase-only filter can be implemented with a polarization modulation device (e.g., ternary filters displayed on a MOD2), simultaneous modulation of continuous phase and binary amplitude has not been shown. In this paper, we propose to use a twisted nematic liquid crystal SLM to implement a phase/amplitude filter. Continuous phase modulation can be achieved by modulating the LC below optical threshold. Besides, a pixel can be turned off (zero transmittance) by applying full voltage across the pixel and by placing an analyzer behind the modulator. This architecture can also be used to display binary-amplitude continuous-phase holograms, which generate better quality images.

Optical correlators have been proposed for many practical applications but have yet to make the transition from the laboratory to the real world. Two basic problems have inhibited the development of these correlators—sensitivity to target orientation and the state-of-the-art in spatial light modulator technology. The U.S. Army Missile Command has been involved in field testing optical correlators for several years. These tests reached a milestone in 1990 with the successful flight of an optical correlator guided missile against a cooperative target. The test program has not stopped with that success, however. A correlator capable of handling changes in target scale and orientation has been designed and is currently under construction. This correlator is based on LCTV spatial light modulators and a smart filtering system. The design of this correlator, its operating characteristics, and data taken by using this correlator will be discussed as part of this presentation.

The modulation characteristics of the liquid crystal televisions found in the Epson Crystal Image video projector have been measured and reported for λ = 0.6328 μm. These characteristics include phase modulation and contrast ratio as a function of both bias voltage and input gray level. Many compact systems for which the LCTVs are candidate spatial light modulators, however, will utilize laser diodes operating in the near infrared. In addition, the phase modulation observed in LCTVs will tend to increase for shorter wavelengths. The purpose of the presentation is to compare the different modulation characteristics of the LCTV across a wide spectral range from blue to the near infrared. The results of these experiments will allow researchers to choose spectral bands in which the LCTV performs best and to evaluate the tradeoffs in operating these devices at other than optimum wavelengths.

Liquid crystal televisions have received extensive attention in literature for use as input and Fourier plane devices in joint transform correlators, and for use in other optical processing architectures requiring television rate inputs. The device has also been used in incoherent optical neural network systems at Penn State University. Recent research investigated the hybrid phase and amplitude modulating properties of the LCTV in a joint transform correlator. A new LCTV made by Epson is the focus of this paper. The hybrid modulation properties of this television will be evaluated and the results presented. Results from applications using the new LCTVs will also be presented.

The spatial light modulator (SLM) is a critical element in most optical processing systems. Different devices on the market today include the Hughes Liquid Crystal Light Valve (LCLV), the Ferroelectric LCLV, the GEC-Marconi LCLV, the Semetex MOSLM, Liquid Crystal Televisions, and the Deformable Mirror Device. The parameters of the above modulators have been evaluated at the Army Missile Command's Photonics and Optical Sciences Labs at Redstone Arsenal in an effort to determine the utility of these modulators as image transducers in optical correlator architectures. This paper will focus on another device perhaps applicable to optical correlators, the Microchannel Spatial Light Modulator (MSLM). The results of speed, maximum resolution, and visibility measurements will be presented.

A first phase demonstration of the capabilities and limitations of an optical correlator in a realistic environment has been completed. The testing was divided into several areas, from laboratory data gathering to a fully functional helicopter-delivered demonstration airframe. The basic research performed has led to three fully fieldable test units which have proven to be rugged and dependable under normal test range conditions. The units were transportable and required no realignment of the optics. Two of the test systems were modular in construction while the third was a 'solid optic' design having optical paths and components contained within a solid glass construction. Two flights have been completed so far, and in both cases the target was identified and tracked, and an airframe guided to target impact.

The performance characteristics of three unique optically-addressed spatial light modulator (SLM) structures have been experimentally investigated. The measured parameters include maximum resolution, visibility, imaging response time, and write light sensitivity. The modulators investigated include two relatively new technologies, the ferroelectric liquid crystal (FLC) SLM from the University of Colorado-Boulder and the amorphous silicon photoconductive twisted nematic liquid crystal SLM from GEC-Marconi Research, and a well established industry benchmark, the Hughes Liquid Crystal Light Valve (LCLV). A comparison of these devices in terms of the above performance parameters is discussed in this communication.

Liquid Crystal Televisions have received extensive attention in the literature for use as input and Fourier plane devices in joint transform correlators, and for use in other optical processing architectures requiring television rate inputs. The device has also been used in incoherent optical neural network systems at Penn State University. Recent research has also investigated the hybrid phase and amplitude modulating properties of the LCTV in a joint transform correlator. These properties will now be applied to the well known Vander Lugt matched filter correlator. The results of employing the LCTV as a phase-only input device for making and addressing photographic matched filters is presented. Experiments using the LCTV as both the input and filter plane modulator in a mixed phase and amplitude mode also is discussed.

A first-phase demonstration of the capabilities and limitations of an optical correlator in a realistic environment has been completed. The testing was divided into several areas, from gathering laboratory data to a fully functional helicopter-delivered demonstration airframe. The basic research performed has led to three fully fieldable test units which have proven to be rugged and dependable under normal test range conditions. The units were transportable and required no realignment of the optics. Two of the test systems were modular in construction while the third was a 'solid optic' design having optical paths and components contained within a solid glass construction. Two flights have been completed so far, and in both cases the target was identified and tracked, and an airframe guided to target impact.

One of the obstacles in real-time holography as well as in optical information processing is the lack of a real-time addressable spatial light modulator that can display a complex function with both amplitude and phase information. In this paper, we describe a novel method that uses two identical 90° twisted nematic liquid crystal displays to implement a continuous phase/amplitude level spatial light modulator. Phase and polarization modulation properties of the twisted nematic liquid crystal cell is due to the modulation of the tilt and the molecules in the vertical direction along the liquid crystal cell structure and the twist in the horizontal plane, respectively. By aligning the incident light to be perpendicular to the front director of the liquid crystal molecules, and inserting an analyzer (in the same direction as the incident light) immediately after the first liquid crystal cell, amplitude-only modulation can be achieved. The light amplitude coming from the first cell is then parallel to the molecular director of the second cell, and phase-only modulation can be achieved by limiting the applied voltage to be below the polarization modulation threshold. The combined modulator is then capable of modulating both amplitude and phase parameters independently by two identical spatial light modulators.

The joint transform architecture is well known in optical processing. Normally object and reference are presented to the system as purely real scenes. If the reference and object are identical, the joint transform power spectrum (JTPS) is the Fourier transform modulated by a cosinusoidal fringe pattern. This pattern is then itself transformed to produce the two correlation signals. Our analysis assumes that reference and object are real but that they are displayed on a device that can only modulate phase. A calculation is done for the resulting power spectrum, and the effect of displaying this power spectrum itself on a device that can only modulate phase is also modeled. Results indicate that good correlation peaks should be experimentally obtained. The effect of using an on-axis stop in the Fourier transform plane is also modeled. The correlation width can be improved greatly with a judicious choice of stops. This can be thought of as an extreme nonlinearity that imitates the behavior of photographic film in a joint transform correlator.1

Wheatstone invented the first stereoscopic display on record in 1834. Numerous approaches to the display of stereo imagery have been demonstrated since; however, all suffer from various drawbacks. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays typically have tight limitations on the position of the viewer's head. We investigate an architecture consisting of two readily available, inexpensive twisted nematic liquid crystal display (TN-LCD) panels sandwiched together to form a compact, rugged stereoscopic display. We describe the theory of operation, the experimental determination of the liquid crystal display modulation characteristics, and modifications to the theory of operation, as a consequence of the experimental results.

The phase modulating capabilities of a commercially available liquid crystal television have been investigated and applied to the joint transform optical correlator architecture. Operating the LCTV in a phase modulating mode requires a much smaller coherent light source while still producing a good joint transform power spectrum and good correlation signals.

In the past 15 years, a dozen or so designs have been proposed for optical computers. Of these, maybe one-third of them have actually been built and only a few of those tested. This paper will give an overview of some of the systems that have been built as well as mention some promising early and current designs that have not been built. Emphasis will be given to application oriented designs that have been built and tested. This means, of course, that the bulk of the paper is devoted to optical correlators.

An investigation is made of means to the standardization of methods for parameter characterization in the cases of spatial light modulators of optically addressed, electrically addressed, amplitude-modulating, and phase-modulating types, with a view to recommendations for future practice. The speed, resolution, and visibility parameters are noted to compare well irrespective of modulator type; phase and amplitude modulating devices cannot be directly compared, however, due to the fundamentally different ways that parameters are measured for each. To be meaningful, the MTF for an optically-addressed device must be accompanied by speed and illumination data. Lifetimes should be specified for all devices.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An optical architecture is proposed that uses two modified liquid-crystal televisions (LCTV's) to control amplitude and phase modulation independently. Two applications in pattern recognition are discussed.

The amplitude- and phase-modulating properties of liquid crystal televisions (LCTVs) are becoming increasingly well known. The Epson Crystal Image video projector is a relatively new TV and uses three liquid crystal panels to encode the red, green, and blue components of the video signal onto the projector light. These panels can be removed for use in optical systems. We present the results from measurements of the phase- and amplitude-modulation properties of one of these LCTV panels.

A novel polarization-encoded two-channel joint transform correlator is described that can produce unity interference modulation, independent of the illumination of the target and the reference.

The phase modulating capabilities of a commercially available liquid crystal television (LCTV) have been investigated and applied to the joint transform optical correlator architecture. Operating the LCTV in a phase modulating mode requires a much smaller coherent light source while still producing a good joint transform power spectrum and good correlation signals.