United States of America As Represented by the Secretary of the Air Force

Other

The United States of America As Represented by the Administrator of the

The United States of America As Represented by the Secretary of

Joseph L Horner

Jacques E Ludman

Bahram Javidi

Charles K Makekau

James R Leger

Henry J Caulfield

Kenneth H Fielding

Thomas L Mikes

Mary A Flavin

John F Walkup

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.

Binary encoding of gray scale nonlinear joint transform correlators

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.

Optical pattern recognition system and method for verifying the

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.

Joint transform correlator using a 4-F lens system to achieve virtual

Method of producing an averaged amplitude mask, for use in conjunction with a phase only filter (pOF) to provide an averaged amplitude matched filter (AAMF) in a Fourier transform optical correlator, involves intensity normalizing a plurality of reference images within a given class of objects, averaging the intensities of the reference images, Fourier transforming the resulting data, and utilizing the resultant amplitude function, exclusive of phase, of the Fourier transform to produce the averaged amplitude filter. A number of such masks are sequentially positioned adjacent the POF to very rapidly determine whether an input image falls within a particular class of objects, or whether the input image is of a particular object within the class.

Averaged amplitude encoded phase-only filters for use in Fourier

In a nonlinear joint transform image correlator, the Fourier transform interference intensity is nonlinearly transformed to provide higher correlation peak intensity and a better defined correlation spot. The correlation signals are determined, for example, in terms of nonlinear characteristics of a spatial light modulator (SLM) at the Fourier plane. The correct phase information of the correlation signal is recovered from the first-order harmonic of the nonlinearly transformed interference intensity, and various types of autocorrelation signals can be produced simply by varying the severity of the nonlinearity and without the need to synthesize specific matched filters. For example, the autocorrelation signal produced by a phase-only matched filter can be obtained by selecting the appropriate nonlinearity.

Nonlinear joint transform optical correlator having varying degrees of

A 2f Fourier transform optical correlator uses two simple, single element lenses, with the second lens performing both quadratic phase term removal and the inverse Fourier transform operation in a compact two-focal-length space. This correlator performs correlations quite well and uses three less lens elements than a prior 2f system, is shorter by a factor of two compared to the standard 4f system, and uses one less lens than the 3f system, while still retaining the variable scale feature.

Compact 2f optical correlator

A simple, low cost, high performance joint Fourier transform correlator, which requires only a single spatial light modulator, is disclosed. Input and reference images are recorded upon a single phase modulating SLM, and a lens produces a first joint Fourier transform of the images upon an electro-optic sensor. The first Fourier transform is binarized and recorded upon the single SLM electronically, and the same lens produces a second Fourier transform to form an image correlation signal at a correlation plane. Also, recordation of the input and reference images and recordation of the joint Fourier transform upon the single SLM may be performed optically rather than electronically.

Single SLM joint transform correaltors

Method allows a first phase-only optical correlator filter function to be written on an amplitude modulating device such as a spatial light modulator (SLM) by applying a bias term to the phase only filter function great enough to obtain a second amplitude encoded filter function, for use with a more economical amplitude responsive SLM.

Amplitude encoded phase-only filters for optical correlators

A modified 2f Fourier transform optical correlator combines a collimation and first Fourier Transform lens into one thin lens. The resulting correlator thus utilizes one less lens relative to the unmodified 2f optical correlator.

Modified compact 2f optical correlator

Method of producing an enhanced output correlation signal from an image matching correlator includes the steps of further transforming data representing an input image to produce a transformed image, multiplying the transformed image by at least one reference filter function representing a reference image to be compared with the input image to produce a product signal, inverse fourier transforming the product signal to product the output correlation signal, and introducing phase distortions within the reference filter function, sufficient to greatly enhance peak values and narrow the area of the correlation peak of the output correlation signal. The method may utilize optical or digital electronic correlation and transformation.

Method of enhancing the signal to noise ratio of an image recognition

A binary phase-only optical correlation system incorporating therein a binary phase-only filter. The binary phase-only optical filter is made by mathematically generating preselected phase-only information by a fast Fourier Transform technique. This generated phase-only information is binarized into a function having two values. This binarized function is utilized to produce a mask which in turn is used in conjunction with an appropriate optical substrate to produce the binary phase-only filter. The manufacture of the binary phase-only filter is substantially easier than the production of a phase-only filter yet virtually the same correlation results when the binary phase-only filter when it is used in an optical correlation system.

Binary phase-only optical correlation system

A capacitance measuring device having an astable multivibrator, a monostable multivibrator, a metering circuit and an overrange circuit. The astable multivibrator generates a repetitive series of evenly spaced pulses which are received by the monostable multivibrator to which a capacitor of unknown value is connected. Each of the pulses initiating a voltage output in the monostable multivibrator which remains in the high state for a length of time linearly proportioal to the value of the unknown capacitor. Thereafter, the voltage output of the monostable multivibrator reverts to the low state and remains at the low state until it receives the next one of the repetitive pulses. The metering means averages the high and low states of the voltage output and provides a pair of average voltage readings indicative of capacitance value of the unknown capacitance. One of the average voltage readings being a true reading of the value of the unknown capacitor and the other of the average voltage readings being a false reading of the value of the unknown capacitor. The overrange circuit provides an indication when the reading of capacitance value is false thereby enabling a user of the device to disregard this reading.

Capacitance measuring device including an overrange circuit

A phase-only optical filter capable of being utilized within a phase-only optical correlation system. The phase-only optical filter is made by mathematically generating preselected phase-only information by a fast Fourier Transform technique. This generated phase-only information is transferred onto an unexposed holographic film. Thereafter, the film is developed and subsequently bleached. The resultant bleached film is the phase-only filter which, when utilized in a correlation system, provides substantially 100% utilization of the source of electromagnetic radiation during the correlation process.

Phase-only optical filter for use in an optical correlation system

A fiber optic cable connector for coupling together a pair of optical fibers having a pair of fixtures, each of the fixtures securing therein a respective optical fiber and having a magnification lens optically aligned with the end of the optical fiber. The lenses and fibers are so positioned relative to each other so as to focus a magnified or enlarged image of the end of each of the fibers to a predetermined position. A fastening means is utilized to removably attach the fixtures together in such a manner that the positions of the enlarged images of the fibers overlap thereby achieving excellent coupling of the adjacent fiber optic ends.

Fiber optic cable connector

A fiber optic directional coupler having a holographic element incorported therein. A single optical signal impinges on the holographic element and is separated into a plurality of individual signals which are coupled to a plurality of individual optical fibers. Only a fraction of the incident electromagnetic radiation incident on the holographic element is transmitted to any one of the plurality of fibers. Reversing the direction of the radiation causes all the energy emanating from the combined plurality of fibers to be coupled to the single receiving fiber.

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Cambridge, MA, United States of America

Joseph L Horner