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

Charles L Woods

Jehad Khoury

Jihad A Khoury

Jonathan S Kane

Philip R Hemmer

Jack Fu

Mark Cronin-Golomb

Thomas J Grycewicz

Peter D Gianino

George Asimellis

Vincent E Ryan

A first lens produces a Fourier transform of the wavefront distorted optical image at the Fourier transform plane. A phase encoded filter is positioned at the transform plane and a second filter is tandemly positioned with respect to the first filter, the second filter having a transmittance which is statistically similar to the reciprocal spatial frequency spectrum of the Fourier transform of the distortion function, to in turn produce an intermediate signal at the transform plane, which is now Fourier transformed by a second lens to recover the optical image having a substantially reduced degree of distortion.

Pseudo deconvolution method of recovering a distorted optical image

A holographic grating is written into a photorefractive erasable holographic member and a light beam having a first wavelength which includes the joint power spectrum of a pair of joint images to be correlated is directed at the photorefractive member to partially erase the grating. A phase conjugate signal from the partially erased grating is then readout and Fourier transformed to produce the correlation output spots.

Incoherent erasure joint transform correlator

An all optical photorefractive holographic joint transform correlator provides a first correlation plane output port using two-beam coupling, and a second correlation plane output port employing four-wave mixing. With appropriate input beam intensity ratios, the first port output is capable of high discrimination, while simultaneously the second port offers a low discrimination output.

Two port nonlinear joint transform correlator

Image derogating optical noise due to light scattering of an object under examination, embedded in a light scattering medium, is substantially reduced by passing a modulated signal laser beam through the scattering medium, and interfering the emerging signal with a coherent modulated reference beam to produce a hologram in a photorefractive member of the object, which in turn is read out of the crystal by a third unmodulated coherent beam to retrieve a clear image of the object. A smart pixel image convertor light valve may be substituted for the photorefractive member.

Imaging in a scattering medium using photon density waves

Image derogating optical noise due to light scattering of an object under amination, embedded in, or positioned in front of a light scattering medium, is substantially reduced by employing a two-dimensional all optical phase sensitive holographic detector and vibrating the light scattering material at an ultra-sonic frequency to produce both signal sidebands and noise sidebands. Homodyne and hetrodyne techniques are used to filter out sidebands due to the light scattering noise and pass the desired signals, thereby to output a clear image of the object free of optical scatter noise. A smart pixel image converter light valve may be substituted for the photorefractive member.

Homodyne and hetrodyne imaging in a light scattering medium

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.

All optical nonlinear joint fourier transform correlator

Limiting quadratic processing and compansion in photorefractive two beam coupling is disclosed. Two-beam coupling in photorefractive barium titanate employs the imaged intensity of the signal to amplify the reference beam while maintaining the phase of the reference beam. The phase distorted signal beam is converted to that of the controlled phase of the reference beam. The high pump limit of amplification in this two-beam coupling device produces an amplitude compressed output to reduce multiplicative noise. Lost contrast of the image is thereafter restored. Beam clean-up of a non-intelligence bearing beam can be carried out by a similar process; a low pass filter consisting of a pinhole plate can be used in place of the second photorefractive crystal in the Fourier plane and only the planar wavefront portion will pass through the pinhole and may be collimated by a lens to provide a cleaned planar output beam.

Photorefractive limiting quadratic processor

An object beam is passed through an aberrating medium to produce a diffraction distorted image therein, which is imaged upon a spatial light modulator. A probe beam measures the phase aberrated wavefront within the aberrating medium and is used to produce an interference pattern which is employed to produce phase encoding signals to be fed back to the spatial light modulator for compensating in part for the phase distortion of the phase aberrated wavefront. The result is an output image having a substantially reduced degree of distortion.

Phase coding technique for one-way image transmission through an

A novelty filter utilizes self-nulling and self-aligning of reflection and transmission phase conjugate beams. A photorefractive crystal is arranged so that the contributions to the phase conjugate are equal and opposite in the steady state to produce destructive interference when the input image is stationary, and thus no output image is displayed. If the image moves, then the gratings will rewrite and erase themselves, each with their own response times, total destructive interference will not occur, and transient enhancement and surpression of the phase conjugate output signal will indicate the direction of motion of the input image.

Photorefractive holographic interference novelty filter

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.

Joint transform correlator using temporal discrimination

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.

Photorefractive two-beam coupling nonlinear joint transform correlator

An associative memory apparatus having a 2f Fourier transform optical correlation configuration wherein the correlation spots produced in the correlation plane are projected back by a mirror through the inverse Fourier transform lens and a phase correction reference image filter to produce the output image representing the best match between the input image and the associative memory reference images. A 4f Fourier transform embodiment projects the correlation spots forward through a second filter and transform means and the output image can be fed back to the input image display SLM to enhance the output image.

Binary phase only filter associative memory

Spatially variable nonlinear optical thresholding in the Fourier plane reduces signal-dependent noise, such as scalar multiplicative noise. Coherent artifact noise reduction by a factor of four is attained using deamplifying photorefractive two-beam coupling. A variable light transmittance threshold across a spatially thresholded light modulating element such as a photorefractive crystal is utilized for this purpose.

Optical signal dependent noise reduction by variable spatial

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.

Quadratic optical processor for reducing multiplicative noise and other

Method of demultiplexing a composite signal light beam includes the steps of directing the composite signal light beam and a reference light beam at a photorefractive material, modulating the reference beam at a frequency about equal to the modulation frequency of a selected signal beam to be demultiplexed, and recovering the phase conjugate signal produced by interference of the reference beam with the composite signal light beam within the photorefractive material. The method also enables optical phase detection of the selected signal beam with respect to the reference beam.

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Stow, MA, United States of America

Charles L Woods