Abstract: A method of verifying the authenticity of an object is disclosed employing a spatial integrating optical correlator. An unreadable and hence non-counterfeitable mask (e.g., a. complex mask or a phase mask) is coupled to the object and the optical correlator compares the mask with a reference mask on which it is scanned over. The correlator produces a correlation spot or image having an intensity which exceeds a given level if the mask is genuine. An alternate embodiment includes a fingerprint or other personalized pattern bonded to the mask, and the fingerprint or other personalized pattern on the card is compared to a reference fingerprint or other personalized pattern of the card holder for added security.

Abstract: In a spatial light modulator of the present invention, a photoconductive layer formed of photoconductive material receives write light having a spatial distribution in its intensity and changes resistivity of the photoconductive material dependently on the spatial distribution in the intensity of the received write light. A liquid crystal layer formed of liquid crystal molecules of nematic phase receives read light and presents birefringence with respect to the received read light. An electric voltage is applied through the photoconductive layer and the liquid crystal layer to thereby produce an electric field in the liquid crystal layer. The photoconductive layer changes the electric field produced in the liquid crystal layer in accordance with the resistivity of the photoconductive material so as to electrically control the birefringence of the liquid crystal molecules.

Abstract: A joint Fourier transform optical correlator is disclosed which can have varying degrees of nonlinearity and yet employ a readily available binary spatial light modulator for producing the correlation output light signal in conjunction with a Fourier transform lens. The nonlinearly transformed joint power spectrum is binarized utilizing a multiple level threshold function which can vary from one pixel to the next.

Abstract: A system and method for increasing the number of bits available for use in a video display system that includes at least one spatial light modulator. The system uses a wheel (30) of three colors, or a color wheel that is clear, including at least one segment (34) which has a lower intensity region, referred to as a neutral density filter. Alternately, the filter could be a liquid crystal controller to control either light amplitude or color. By using a lower intensity region, the amount of time available to process the least significant bit of the data sample is lengthened, thereby eliminating the constraint on the number of bits available for display.

Abstract: A method is provided for normalizing correlation data from a holographic correlator. After a sequence of object image patterns are recorded in an angularly multiplexed hologram, the entire volume hologram contents are read out with a uniform (plane wave) object beam. The plane wave readout produces an array of spots at a correlation plane, with the intensity of each spot representing the strength of the recorded hologram for the corresponding stored image pattern. The spot intensity values are accurately detected and stored as normalization factors. Holographic correlation output array values produced by parallel comparison of an input object pattern with the stored image patterns are then divided by the corresponding normalization factors. The resulting normalized correlation output accurately represents the true degree of correlation between the input object pattern and the stored image patterns by eliminating the uncertainty factor.

Abstract: An optical correlator is disclosed that compares signals of interest agai selected reference signals stored in holograms both of which are imaged onto a spatial light modulator comprising electron trapping material. The cooperative action of the light from the hologram and the light from a delayed line causes the spatial light modulator to produce signals that are proportional to the correspondence between the signals of interest and the reference signals.

Abstract: An optical probe collects light responses from a specimen that selectively and preferentially emanates from a localized volume element within the sample, with illumination irradiance and collection efficiency both dropping off away from the localized volume element, and a processor applies a vector or matrix transform to collected responses to produce an output. The optics provide high peak illumination and high collection efficiency which both overlap in small volume elements that are limited in length, width or depth to correspond to a structure or process of the specimen so that the collected spectra or other responses have high signal strength and enhanced correlation values to small or otherwise inaccessible or masked effects present in macroscopic or submacroscopic regions.

Abstract: A method and apparatus for implementation of neural networks for face recognition is presented. A nonlinear filter or a nonlinear joint transform correlator (JTC) employs a supervised perceptron learning algorithm in a two-layer neural network for real-time face recognition. The nonlinear filter is generally implemented electronically, while the nonlinear joint transform correlator is generally implemented optically. The system implements perception learning to train with a sequence of facial images and then classifies a distorted input image in real-time. Computer simulations and optical experimental results show that the system can identify the input with the probability of error less than 3%. By using time multiplexing of the input image under investigation, that is, using more than one input image, the probability of error for classification can be reduced to zero.

Abstract: An optical image processor includes a nonlinear active gain medium for recording an interference pattern that corresponds to the Fourier transform of an input image or the multiplicative product of the Fourier transforms of two respective input images.

Abstract: A method and system for searching for a given sequence in a data base having a multitude of reference sequences stored or identified therein. In accordance with this method, a light beam is modulated with patterns representing the reference sequences, and with a pattern representing the given sequence, and a correlation signal is generated representing the correlation of the reference and given sequences.Optical diffraction patterns may be used to represent the given and reference sequences. In one embodiment, a multitude of first diffraction patterns, each one representing the given sequence, are formed in an optical medium, and a light beam is modulated with each of those multitude of diffraction patterns to form a multi-channel signal beam. Each channel of that beam is then modulated with a respective one second diffraction pattern representing one of the reference sequences to form a multi-channel correlation beam.

Abstract: An amplitude encoded lens function signal, similar to a zone plate, is formed in the transform plane of a chirp encoded joint transform correlator. CCD correlation spot light sensor is separated from the transform plane by the focal length of the encoded lens function, and generates the desired output correlation spot. As a result, no prior art inverse transform lens need be provided, which simplifies the design. Further simplification is attainable in a low noise commercial image matching environment by eliminating the CCD correlation spot sensor entirely, and verifying an input image/reference image close match by using the eye of an operator to check for the presence of the visible zone plate, indicative of such a match.

Abstract: A Fourier transform optical apparatus for optically Fourier transforming an input image includes a spatial light modulator for displaying an input image, a light source for irradiating the input image on the spatial light modulator, a first convex lens and a first concave lens arranged near the spatial light modulator and a second convex lens arranged at the composite focal plane of the first convex lens and first concave lens. The respective focal lengths of these three lenses are determined to satisfy conditions such that a light ray passing an intersection of the spatial light modulator and an optical axis of the Fourier transform optical apparatus becomes a light ray parallel to the optical axis after passing the second convex lens and a light ray incident to the first convex lens in parallel to the optical axis is focused at the composite focal point of the first convex lens, first concave lens and the second convex lens.

Abstract: An object of the invention is to provide a method and a apparatus for optical pattern recognition capable of accurately comparing and identifying a reference image accurately at a real-time even when the input image rotates or its size changes by being compared with a reference image that is a desirous target. The method and apparatus comprise the processes of; steps (6, 11) for independently obtaining a lower-frequency component and a higher-frequency component from a joint Fourier transform image 5 of the reference image 4 and the input image 3; steps (10, 15) for calculating correlation coefficients respectively from the lower-frequency component and the higher-frequency component; step (16) for obtaining a ratio of the respective correlation coefficients; and step (19) for identifying and comparing a correlation coefficient ratio of the two same reference images to be required with a correlation coefficient ratio obtained from step (16).

Abstract: An optical image correlator includes a photorefractive medium for recording an interference pattern that corresponds to the Fourier transform of an input image or the multiplicative product of the Fourier transforms of two respective input images. In contrast to correlators of the prior art, the correlator described here includes a semi-insulating, multiple quantum well device as the photorefractive medium.

Abstract: A fully parallel, self-aligning, nonlinear and all optical joint transform correlator utilizes a photorefractive four wave mixer positioned to record the joint transform spectrum interfering with a reference beam together with a phase conjugator which directs a readout beam at the four wave mixer. The signal readout of the mixer is Fourier transformed and can be recorded upon an image sensor to detect the correlation spots indicating the degree of similarity of the two input images.

Abstract: An high-speed, high-resolution optical pattern recognition system which automatically recognizes or measures a specified pattern from two-dimensional images comprises an image display device for displaying at least one reference image including at least one target and at least one input image, a device including a laser diode having an oscillation wavelength less than 900 nm for converting the at least one reference image and the at least one input image into a coherent image, a Fourier transform lens for optically Fourier transforming the coherent image to produce a joint Fourier-transformed image, an optically addressed ferroelectric liquid crystal spatial light modulator having no light reflection layer, a device for converting the joint Fourier-transformed image into an intensity distribution image and displaying the intensity distribution image on the optically addressed spatial light modulator, and a device including a laser diode having an oscillation wavelength longer than 660 nm for reading the inten

Abstract: A spatial Fourier transforming apparatus jointly Fourier transforms a plurality of input images to obtain a Joint Fourier transform image of the plurality of input images. The apparatus comprises: input means for inputting a plurality of input images; a mask member having a plurality of aperture edges for defining a plurality of apertures each for transmitting a part of a corresponding one of the plurality of input images, the plurality of aperture edges having low correlation; and Fourier transforming means for jointly Fourier transforming the parts of the plurality of input images having passed through the plurality of apertures and for obtaining a Joint Fourier Transform image of the plurality of input images.

Abstract: An arrangement for optical autocorrelation of laser speckle photography (LSP) photographs or particle image velocimetry (PIV) photographs using optical Fourier transforms is disclosed. The object of providing an electro-optical arrangement for optical correlation of LSP film recordings and PIV film recordings which is simple to produce and accurate is met by using an optically addressable liquid crystal SLM (spatial light modulator) for producing the Young's fringe patterns which contains a uniaxial double-refracting liquid crystal layer and is read out with linearly polarized light of a laser light source, wherein the polarization direction of the laser light source on the readout side coincides with the extraordinary semi-axis of the refractive index ellipsoid of the liquid crystal layer.

Abstract: A rangefinding/autofocusing apparatus utilizes a joint transform correlator of a Fourier correlation optical system. A pair of imaging lens systems form a pair of object input images. A lens driving mechanism drives the imaging lens systems in a parallel manner. The pair of object input images are recorded for display. A reference input image is displayed concurrently along with the recorded object input images in an offset relation relative to each other. A photodetector disposed on the correlation plane of the Fourier correlation optical system detects correlation peaks corresponding to a correlation coefficient of the pair of displayed object input images to measure an interval between the detected correlation peaks. The photodetector also detects correlation peaks corresponding to a correlation coefficient of the reference input image and the object input images to determine a correlation between the reference image and the object.

Abstract: An SLM rotates linearly polarized incident light, produced by a first polarizer, through a continuous range of angles up to a maximum angle, eg. seventy degrees. The second output polarizer is oriented orthogonally with respect to the angular thirty-five degrees bisector between the first polarization state at zero degrees rotation and the maximum possible angular rotation at seventy degrees and accordingly, a single SLM can be operated in an amplitude coupled binary phase mode.

Abstract: An optical signal processor which employs a coherent light source, two spatial light modulators and a beam splitter. Light is from the source is reflected from the beam splitter and sent to a first spatial light modulator, then sent through the beam splitter, a Fourier transform is performed and the transformed light is then reflected from the second spacial light modulator. The light form the second spacial light modulator is then inverse transformed and returned to the beam splitter where it is reflected to a readout detector. The signal read out is the correlation map between an input image from the first modulator and a filter image of the second modulator.

Abstract: A joint transform correlator has modulators for temporally modulating a first optical input signal at a first frequency and a second optical input signal at a second frequency. An image sensor in the Fourier plane forms a product signal modulated by temporal sum and difference frequencies of the first and second frequencies. The product signal is thereafter demodulated at the temporal sum or difference frequency and the resulting optical signal is inverse Fourier transformed to recover the desired cross correlation signals.

Abstract: A pattern recognition apparatus and a method for operating same. The apparatus includes a volume holographic medium (4) having a plurality of Fourier-space volume holograms representing pattern templates stored within. The apparatus further includes a spatial light modulator (1) and a phase encoder (2). The phase encoder has an output optically coupled to the medium by a first Fourier transform lens (3). The spatial light modulator spatially modulates a spatially uniform laser beam (7) in accordance with an unknown pattern. The two-dimensional phase encoder causes the spatially modulated laser beam to be spatially distributed prior to application to the medium. The apparatus also includes a detector (6, 11) having an input optically coupled by a second Fourier transform lens (5) means to an angular spectrum of plane waves generated by the medium in response to the output of the spatial modulator, phase encoder, and first Fourier lens.

Abstract: An all-optical nonlinear joint transform correlator has been implemented for the first time without using a spatial light modulator and digital processing in the Fourier plane. The correlator utilizes energy transfer from two-beam coupling in the Fourier plane. A compressional nonlinearity in the hard-clipped regime is implemented by pumping a weak plane wave with the intense joint spectrum of the reference and signal images. Operation of this device rivals or exceeds that of the phase-only filter for detecting objects in cluttered noise. Experimental results are compared with both plane wave and beam propagation simulations.

Abstract: A method of verifying the authenticity of an object is disclosed preferrably employing a joint transform coherent optical processor. An unreadable and hence non-counterfeitable phase mask is coupled to the object and the optical processor compares the phase mask with a reference phase mask having the same phase code thereon. The processor produces a correlation spot having an intensity which exceeds a given level if the phase mask is genuine. A highly secure ID or credit card also carries a fingerprint bonded to the phase mask, and the fingerprint on the card is compared to a reference fingerprint of the card holder for added security.

Abstract: A system and method of optical correlation that avoids bias level terms in the optical correlation output. In the system and method, two coherent polarized component beams having frequencies f.sub.1 and f.sub.2 are derived from a light source. Portions of these component beams are converted to a reference electrical signal having a frequency .DELTA.f=f.sub.2 -f.sub.1. The sum f.sub.1 +f.sub.2 of the component beams is correlated under the control of a multiple of the reference electrical signal. The Fourier transform of the amplitude of the correlated light is projected and detected on a detection plane.

Abstract: A micro-optical shutter array (92, 102) having a number of tiny shutters (10), which revolve so as to intermittently block light from a via (12), and which may be operated in either a stepping or continuous motion. The array (92, 102) may be batch manufactured using integrated circuit fabrication techniques. For each shutter, a via (12) is etched through a substrate (11). A rotor (13, 43, 53, 63) with at least one opening is fabricated over the via (12), such that as the rotor (13, 43, 53, 63) turns, radiation transmitted through the via (12) is selectively blocked or not blocked.

Abstract: In an optical correlator system having reflective and transmissive optical components positioned along a folded and segmented optical axis or path, one or more optical path extenders are provided for selected optical path segments that require operative path length adjustment so that an electromagnetic radiation beam, which traverses the folded optical path with selected information imparted into and detected from the beam, can be imaged upon a defined and maximum usable area or region both on the reflective components and on an end detector component.

Abstract: A 4-f lens system is positioned over one half of the joint input image presentation SLM device of a conventional joint transform correlator (JTC). An image displacement lens is positioned in the Fourier transform plane of the 4-f correlator and can shift the virtual displacement of the reference image plane relative to the input image plane. By the appropriate choice of this lens, any virtual displacement can be achieved to provide for substantial design flexibility of the JTC.

Abstract: A neural network has inputs formed by square array of optical modulators M.sub.ij and outputs by optical detectors D.sub.ij coupled to threshold comparators. A holographic plate includes a spatial modulator whose elements are controlled by a controller to form an array of optical beams from a coherent optical source. Each optical beam optically interconnects a modulator M.sub.ij with a respective detector D.sub.ij. The weight values of the neural network are provided by the intensities of the optical beams. This obviates the need for an optical weighting mask between an array of light emitting diodes and a detector array allowing a higher density of lower power consumption components and reprogrammability of the network.

Abstract: An optical correlator uses ferroelectric liquid crystal spatial light modulators (FLC-SLM's) in both the reference and filter planes. The SLM's include an electrically addressable memory to store images in the form a two-dimensional array of reflective pixels beneath the FLC layer. The SLM's selectively rotate the polarization of the light reflected by each pixel in accordance with the stored image. In particular, a laser produces a polarized beam that is directed through a first polarizing beamsplitter and onto the reference SLM. This beamsplitter blocks unmodulated light reflected by the reference SLM and transmits modulated light through a set of Fourier tranform lenses. The resulting beam is directed through a second polarizing beam splitter onto a filter SLM that has been programmed with the complex conjugate of the Fourier transform of a desired target image.

Abstract: A Fourier transform lens assembly suited for use in an optical information processor includes a first lens group having a positive power, a second lens group having a negative power disposed on one side of the first lens group, and a third lens group having a positive power disposed on the side opposite to the first lens group with respect to the second lens group. The distance between a front focal plane and a back focal plane of the Fourier transform lens assembly is less than two times a focal length of the Fourier transform lens assembly.

Abstract: A spatial frequency filter used in a pattern defect detection device, including a pattern which includes a black spot having a diameter expanded by a controlled amount in comparison with the diameter of a black spot on a photosensitive plate obtained by exposure by diffracted light from a pattern on a model specimen.

Abstract: A new type of optical correlator performs motion detection or background clutter suppression and correlation simultaneously in a single photorefractive crystal, and is useful for moving target identification and tracking and for stationary clutter rejection. The correlation is of the VanderLugt type and the motion detection or background clutter suppression is based on the erasing property of photorefractive crystals.

Abstract: A joint transform optical correlator is disclosed having an optical path length adjustment technique for causing a first optical path length between the reference image plane and the first Fourier transform lens to differ from a second optical path length between the input image plane and the first Fourier transform lens by an amount whereby the second Fourier transform lens separates the desired cross-correlation signals from the undesired signals to enhance the performance and reliability of the correlator.

Abstract: A visual recognition apparatus for use in, for example, a robot requires an optical information processor for performing image processing or image recognition. The optical information processor includes a first spatial light modulator for displaying an input image, a first lens having a front focal plane on which the first spatial light modulator is positioned, a second spatial light modulator for displaying at least one optical filter, a second lens having a front focal plane on which the second spatial light modulator is positioned, and a third lens having a front focal plane on which a rear focal plane of the second lens lies. The optical information processor also includes a beam splitter for combining together light transmitted through the first lens with light transmitted through the third lens, and a fourth lens having a front focal plane on which both a rear focal plane of the first lens and a rear focal plane of the third lens generally lie.

Abstract: A degenerate four-wave mixing arrangement employs a photorefractive crystal as a real time holographic recording medium to record a hologram of the noisy optical signal. The signal passes through the crystal and is phase conjugated by a self pumped barium titanate phase conjugator, and the resulting phase conjugate beam reads out the hologram and multiplicative noise is substantially reduced in the optical output signal.

Abstract: An optical correlation unit for correlating the images of an inspection object and a reference object. The unit uses two phase modulating reflective spatial light modulators. A first spatial light modulator receives electronic input in the form of image data representing the inspection object. It modulates incoming light with this input and reflects the modulated output to a first Fourier transform lens. This lens provides the optical input to a second spatial light modulator, whose electronic input is transform data representing the complex conjugate of the Fourier transform of the reference image. The electronic input modulates the optical input, resulting in the Fourier product of the two images, which is then transformed to provide correlation data.

Abstract: A signal processing device used for processing images including an optical correlator combined with a neuonal processor.

Abstract: An optical correlator system having a plurality of reflective optical components, both active and passive, positioned (1) between a source of electromagnetic radiation, such as a visible beam of coherent light, and an output detector array, and (2) around an asymmetrical perimeter of a planar support body to develop an asymmetrically folded optical axis or path wholly within the body where the path is traversed by the beam SO THAT information processed by the active optical components along the optical path and imparted to the optical beam enable the optical detection of an unknown object at the detector array which is then subject to an identification process.

Abstract: In a joint transform correlator utilizing a spatial optic modulator, depending on the light intensity of each correlation peak obtained from optical correlation processing between at least one reference image and at least one input image, the light intensity passing through each reference image corresponding to each correlation peak is substantially adjusted so as to constitute a feedback system. By such construction, when processing a relatively large number of input or reference images, the correlator can avoid failure of recognition due to the reduction of light intensity of the correlation peaks and can avoid erroneous recognition to enable fast pattern recognition.

Abstract: A self amplifying optical pattern recognizer includes a geometric system configuration similar to that of a Vander Lugt holographic matched filter configuration with a photorefractive crystal specifically oriented with respect to the input beams. An extraordinarily polarized, spherically converging object image beam is formed by laser illumination of an input object image and applied through a photorefractive crystal, such as a barium titanite (BaTiO.sub.3) crystal. A volume or thin-film difORIGIN OF THE INVENTIONThe invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected to retain title.

Abstract: A video-rate correlator constructed with a phase-only spatial light modulator and video camera. The phases of the Fourier spectra of a test and reference image are measured by real-time fringe scanning interferometry. The two phase images are then electronically subtracted. The optical Fourier transform of this difference produces the phase-only correlation response. This correlator is real-time adaptive, in that it uses live imagery, and neither the test or reference images need any preprocessing off-line. Especially small optical layouts, which also efficiently use light for correlation, can be configured through the use of specific embodiments, which use only a single phase-only spatial light modulator and Fourier transform lens.

Abstract: In a joint transform correlator, a technique that performs a correlation processing between two-dimensional images by using a coherent beam, this invention forms a feedback system in which two-dimensional correlation coefficients between at least one reference image and at least one signal image obtained as a result of a correlation processing are input to a linear or non-linear transfer function and in which the intensities of light passing through the reference images corresponding to the correlation coefficients are virtually changed according to the output of the transfer function. And then in this condition a similar correlation processing is performed. This loop of processing is repeated.

Abstract: An associative optical memory including an input SLM in the form of an edge enhanced LCLV and a pair of memory SLMs in the form of LCTVs forms a matrix array of an input image which is cross correlated with a matrix array of stored images. The correlation product is detected and non-linearly amplified to illuminate a replica of the stored image array to select the stored image correlating with the input image. The LCLV is edge enhanced by reducing the bias frequency and voltage and rotating its orientation. The edge enhancement and non-linearity of the photodetection improves the orthogonality of the stored images. The illumination of the replicate stored image provides a clean stored image, uncontaminated by the image comparison process.

Abstract: A pattern recognition method and apparatus wherein an optical correlator and a feedback light path are provided. In the optical correlator, an input pattern whose image is formed on a first spatial light modulator (valve) is read by the irradiation of coherent light, and an image of a correlation peak image of this reading light is formed by the use of a correlation filter on which a plurality of reference patterns are recorded in the form of modified patterns. In the feedback light path, the correlation peak image is formed on a second spatial light modulator (valve), the correlation peak image is read out by the irradiation of coherent light, and the light having read the correlation image is made to pass a display filter on which display reference patterns are recorded.

Abstract: The present invention provides a receptor system in which laser light from a laser source is directed onto a sample, the transmitted light from which is photomixed by a half mirror with laser light different in frequency from laser light from a local oscillator source, and the photomixed light is received by a receptor element dividing a light propagating zone into a plurality of sub-zones, said receptor element having an exit end, at which a spatial zone, which is defined between different points and in which interference occurs, is limited within a spatially resolvable minimum unit, to form a Fraunhofer diffraction image, whereby the 0 order diffraction image of the Fraunhofer diffraction image is partly or wholly detected by a photodetector, or alternatively a diffraction image at most n times as large as the 0 order spectrum is detected by the photodetector.

Abstract: An electromagnetic signal processor which uses an inhomogeneously broadened absorbing material to store data for long periods of time and which is able to process an uninterrupted signal. A spectral interference pattern created by the interference of at least two input pulses of electromagnetic radiation is stored in the absorbing medium. The pattern is fixed in the medium to allow for uninterrupted processing of signal data. The fixed pattern employed in such a processor could be reprogrammed by either reversing the gating process used to program the absorbing medium or by spatially directing the electromagnetic beams to a different portion of the material.

Abstract: A method of obtaining a correlation between a pattern to be identified and a number of reference patterns by irradiating and displaying the pattern to be identified and the reference patterns on an optical display plane, thereby producing a complex optical amplitude distribution. This distribution is Fourier-transformed to produce a first power spectrum corresponding to the light intensity distribution of its Fourier transformation patterns. The patterns are again irradiated based upon the first power spectrum and a second Fourier transform is performed to produce a second power spectrum which is the light intensity distribution of the second Fourier transformation pattern. The area of this distribution is restricted by controlling the transmittance or the reflectance of each of the portions of the display plane.

Abstract: An optical correlator system for encoding a complex optical image onto a erent beam of light such as a laser and comparing it with a reference complex image. One embodiment of the invention encodes phase only information of the complex image onto the coherent beam of light by means of a liquid crystal television receiver. The light beam is passed through the liquid crystal television receiver, whose pixels are manipulated to provide phase information concerning the image. A second embodiment of the invention encodes both phase and amplitude components of a complex image onto the coherent beam of light such as a laser beam. Either or both encodings are utilized in the optical correlator system.