Jihad Khoury

All optical nonlinear joint fourier transform correlator

We present the first all-optical nonlinear joint transform correlator based on a square-law receiver in the Fourier plane. Our device uses a photorefractive limiting quadratic processor. The compressional nonlinearity associated with the transfer function of the limiting quadratic processor enables the correlator to detect signals embedded in Gaussian and non-Gaussian noise. In the limiting region this device correlates the phase-only information of the input. This is the first time to our knowledge that photorefractives or real-time holography has been used in the correlation of the phase-only information. We demonstrate the operation of this device experimentally, and we evaluate its performance throughcomputer simulation for various forms of noise.

Photorefractive holographic interference novelty filter

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.

Quadratic processing and nonlinear optical phase rectification in noise reduction

Optical spatial phase rectification by limiting quadratic processing in photorefractive two-beam coupling is proposed and demonstrated. We use this limiting quadratic processor to reduce complex multiplicative noise. The principle of compansion (compression and expansion) from serial communication theory is introduced for the first time to our knowledge in parallel optical signal processing. In addition the effect of two-beam coupling compression on the efficiency of beam cleanup is illustrated experimentally and optimized through computer simulation.

Synthetic aperture radar image correlation by use of preprocessing for enhancement of scattering centers

We demonstrate that a significant improvement can be obtained in the recognition of complicated synthetic aperture radar images taken from the Moving and Stationary Target Acquisitions and Recognition database. These images typically have a low number of scattering centers and high noise. We first preprocess the images and the templates formed from them so that their scattering centers are enhanced. Our technique can produce high-quality performance in several correlation criteria. For realistic automatic target recognition systems, our approach should make it easy to implement optical recognition systems with binarized data for many different types of correlation filter and should have a great effect on feeding data-compressed (binarized) information into either digital or optical processors.

TWO-PORT PHOTOREFRACTIVE JOINT-TRANSFORM CORRELATOR

We present what is to our knowledge the first quantitative analysis of the dual optimality that can be achieved in the all-optical two-port photorefractive joint-transform correlator. We determine the operating region where these ports have complementary performance: the first port performs well for non-Gaussian clutter noise, and the second port is optimal for additive Gaussian noise. Dual optimality is achieved without the performance compromise of the optimal trade-off filter approach.

Phase-restricted heterogeneous correlation

We introduce a new phase-restricted algorithm for producing a heterogeneous correlation filter that permits new in-class members to be added without changing the phase of the filter. This heterogeneous correlation filter uses amplitude modulation both to enhance in-class cross correlations and to suppress selected out-of-class correlations. This new algorithm should substantially improve the performance of existing class-associative correlators and improve their operation.

Binary phase only filter associative memory

An associative memory is implemented using a binary phase-only filter as the memory element. In the current architecture, if the input contains any part of the set of stored memories, then the entire set is retrieved at the output. In addition, the sharp autocorrelation peak and the high signal-to-noise ratio allows operation without necessitating a thresholding device.

Companding nonlinearities in optical signal processing

Compression, expansion and rectification are well established noise reduction techniques in digital electronic communication systems. Photorefractive crystals provide high-resolution, real-time, low-power, parallel-nonlinear optical devices for performing these operations, and, in the last decade, considerable progress has been achieved in designing photorefractive devices with various functions and performance. We have recently proposed and demonstrated several photorefractive nonlinear techniques for reducing the following forms of noise: (1) additive random noise; (2) additive signal dependent noise; and (3) multiplicative zero mean complex noise. These noniinear approaches to noise reduction are not limited to photorefractives and may be implemented by alternative optical nonlinear technologies. In this paper, we present general optical nonlinear models for these noise reduction techniques and compare them with our photorefractive experiments.