Mehjabin Sultana Monjur

Hybrid optoelectronic correlator architecture for shift-invariant target recognition

In this paper, we present theoretical details and the underlying architecture of a hybrid optoelectronic correlator (HOC) that correlates images using spatial light modulators (SLMs), detector arrays, and field programmable gate array (FPGA). The proposed architecture bypasses the need for nonlinear materials such as photorefractive polymer films by using detectors instead, and the phase information is yet conserved by the interference of plane waves with the images. However, the output of such an HOC has four terms: two convolution signals and two cross-correlation signals. By implementing a phase stabilization and scanning circuit, the convolution terms can be eliminated, so that the behavior of an HOC becomes essentially identical to that of a conventional holographic correlator (CHC). To achieve the ultimate speed of such a correlator, we also propose an integrated graphic processing unit, which would perform all the electrical processes in a parallel manner. The HOC architecture along with the phase stabilization technique would thus be as good as a CHC, capable of high-speed image recognition in a translation-invariant manner.

Incorporation of polar Mellin transform in a hybrid optoelectronic correlator for scale and rotation invariant target recognition

In this paper, we show that our proposed hybrid optoelectronic correlator (HOC), which correlates images using spatial light modulators (SLMs), detectors, and field-programmable gate arrays (FPGAs), is capable of detecting objects in a scale and rotation invariant manner, along with the shift invariance feature, by incorporating polar Mellin transform (PMT). For realistic images, we cut out a small circle at the center of the Fourier transform domain, as required for PMT, and illustrate how this process corresponds to correlating images with real and imaginary parts. Furthermore, we show how to carry out shift, rotation, and scale invariant detection of multiple matching objects simultaneously, a process previously thought to be incompatible with PMT-based correlators. We present results of numerical simulations to validate the concepts.

All optical three dimensional spatio-temporal correlator for automatic event recognition using a multiphoton atomic system

Abstract We describe an automatic event recognition (AER) system based on a three-dimensional spatio-temporal correlator (STC) that combines the techniques of holographic correlation and photon echo based temporal pattern recognition. The STC is shift invariant in space and time. It can be used to recognize rapidly an event (e.g., a short video clip) that may be present in a large video file, and determine the temporal location of the event. Using polar Mellin transform, it is possible to realize an STC that is also scale and rotation invariant spatially. Numerical simulation results of such a system are presented using quantum mechanical equations of evolution. For this simulation we have used the model of an idealized, decay-free two level system of atoms with an inhomogeneous broadening that is larger than the inverse of the temporal resolution of the data stream. We show how such a system can be realized by using a lambda-type three level system in atomic vapor, via adiabatic elimination of the intermediate state. We have also developed analytically a three dimensional transfer function of the system, and shown that it agrees closely with the results obtained via explicit simulation of the atomic response. The analytical transfer function can be used to determine the response of an STC very rapidly. In addition to the correlation signal, other nonlinear terms appear in the explicit numerical model. These terms are also verified by the analytical model. We describe how the AER can be operated in a manner such that the correlation signal remains unaffected by the additional nonlinear terms. We also show how such a practical STC can be realized using a combination of a porous-glass based Rb vapor cell, a holographic video disc, and a lithium niobate crystal.

Analytical transfer function for the nonlinear response of a resonant medium in the spatio-temporal Fourier-transform domain

The nonlinear response of a resonant medium has many applications. To model and find the response of such a medium requires solving the Schrodinger equation (SE), which is a computationally extensive task. In this paper, we develop an analytical model to find the response of a resonant medium due to an applied field by employing the spatio-temporal Fourier-transform (STFT)–domain-based transfer function. A key feature of this approach is the use of the resonant excitation approximation (REA), which amounts to assuming that a group of atoms (or other quantum systems) within a volume element in the STFT domain are excited by only the corresponding volume element in the STFT domain of the field. We first derive the one-dimensional transfer function using an inhomogeneously broadened atomic medium under the REA. Then, we develop the three-dimensional transfer function and show that the analytical model agrees closely with the results obtained via an explicit simulation of the atomic response. As a practical example of the analytical model, we show that it can be used to model a spatio-temporal-correlator-based automatic event recognition system at a speed that is many orders of magnitude faster than solving the SE.

Experimental demonstration of the hybrid opto-electronic correlator for target recognition

Optical target recognition using correlators is an important technique for fast verification and identification of images. The hybrid opto-electronic correlator (HOC) recently proposed by us bypasses the need for nonlinear materials such as photorefractive polymer films by using detectors instead, and the phase information is yet conserved by the interference of plane waves with the images. In this paper, we demonstrate experimentally the basic working principle of the HOC architecture using currently available technologies. For matched reference and query images, the output signal shows a sharp peak, indicating a match is found. For an unmatched case, a much lower peak value is observed, indicating no match. We also demonstrate the dependence of the output signal on the phases of the interfering plane waves and describe a technique using an interferometer and a servo for optimizing the output signal. As such, the work reported here paves the way for further development of the HOC for practical applications.

Stabilization, Tuning and Optimization of Relative Phases of Reference Interferometers in a Hybrid Optoelectronic Correlator

We show that in a hybrid optoelectronic correlator, the output signal depends on the relative and absolute phases of the two optical beams used to record interferences, and describe how to control and optimize these phases.