Two principal coherent photonic architectures have been described for correlation-based pattern recognition; Vander Lugt Correlation (VLC) and joint transform correlation (JTC). Both originated in the 1960's, followed by many variations on each. In this paper we describe a new hybrid photonic/electronic correlator architecture with advantages over this prior art. For example, both the VLC and JTC employ at least two spatial light modulators (SLMs) which require precise optical alignment, resulting in sensitivity to mechanical vibration. While such systems can be ruggedised this is complicated and costly. At DERA Malvern we have built and demonstrated a new photonic correlator whose construction and operation are shown in Figure 1. This uses just one SLM and is therefore simpler to align, and is more compact and rugged than either the VLC or the JTC. It exploits fully the complementary benefits of photonic signal processing and digital signal processing (DSP).
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