Hybrid optoelectronic correlator architecture for shift-invariant target recognition

Abstract

In this paper, we present theoretical details and the underlying architecture of a hybrid optoelectronic correlator that correlates images using Spatial Light Modulators (SLM), 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 a Hybrid Opto-electronic Correlator (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

“…7. As shown in ref [7], the HOC is capable of shiftinvariant image recognition, in the same manner as what is achieved with a conventional holographic correlator (CHC). However, the actual architecture is very different, requiring many intermediate steps, servos and post processing.…”

“…Experimental efforts are underway in our laboratory to demonstrate these capabilities of the HOC using bulk components. Efforts are also underway to develop an integrated graphic processing unit (IGPU) [7] in order to realize a high-speed version of the HOC.…”

“…In our architecture, we have convolution terms (T 1 and T 2 ) in addition to cross-correlation terms (T 3 and T 4 ). The convolution terms can be washed out by implementing a phase stabilization and scanning technique in the HOC architecture which has been discussed in details in ref [7].…”

“…Thus, assuming 7 that the contributions from T 1 and T 2 are eliminated via the combination of phase scanning and low pass filtering [7], the final FPA signal can be expressed as: (10) It is useful to consider two different scenarios in order to interpret the information one can glean from this signal.…”

“…A JTC of this type suffers from many practical problems and constraints. As an alternative, we recently proposed a hybrid optoelectronic correlator (HOC) [7] where the nonlinearity provided by the JTC medium is replaced by the non-linearity of high-speed detectors.…”