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.

Investigation of frequency invariance in automated event recognition using resonant atomic media

“…To mathematically depict the process of correlation, the transfer function of the temporal correlator is derived through a frequency domain analysis, as described in references [ 2,13 ]. The three temporal signals are defined as A(t), B(t) and C(t) for the recording pulse, the query signal, and the reference signal, respectively.…”

“…The spatio-temporal holographic correlator (STHC) 2 is an opto-atomic device that was recently proposed to perform AER. This system combines a 2D optical image correlator with a 1D atomic temporal correlator, which allows it to perform correlations efficiently in the spatial and temporal domains simultaneously.…”

Optical Correlators for Cryptosystems and Image Recognition: A Review

“…It presents both analogical and digital versions. In one of the analogical approaches [ 117 ], a 3D STC was proposed, using a combination between holographic correlation and temporal pattern recognition, the latter one based on photon echo. Thus, an AER (automatic event recognition) system was obtained, that achieved spatio-temporal invariance to shift, with the further possibility to also achieve spatial invariance to both rotation and scale, by using the polar Mellin transform.…”

“…The system was validated by numerical simulations. The authors also presented a method for obtaining a practical version of the device [ 117 ]. The same group developed an analytical method, using the STFT (spatio-temporal Fourier transform), and obtained an improvement with many orders of magnitude of the response speed of an AER system based on the STC, as compared to numerical methods based on the Schrödinger equation [ 118 ].…”