Optical Signal Processing

13

Space-Integrating Correlators

13.1.   INTRODUCTION

In Chapter 5, we described matched filtering techniques for the detection of two-dimensional signals. The basic technique is to correlate a received signal with a known signal which is stored either as a matched filter or as a reference function. These system architectures are of the space-integrating type because light that contributes to the correlation peak is integrated over a well-defined spatial region. In this chapter we examine space-integrating correlators that use acousto-optic cells for processing wideband time signals in real time. Because correlation gain, in general, is equal to the space or time bandwidth product of the signal and because the time bandwidth product for most acousto-optic cells is of the order of 1000–2000, the correlation gain is of the order of 30–33 dB, an acceptable figure for processing signals used in some radar systems and communication systems. In Chapter 14, we describe time-integrating architectures that provide more correlation gain.

An early reference to the use of acousto-optic cells for correlation was made by Rosenthal (86). Because Rosenthal described correlation only briefly, his publication did not receive as widespread attention as did the work of Slobodin (95) and Arm et al. (111), whose early work related mostly to processing radar signals. Later papers by Felstead (112, 113), by Atzeni and Pantani (114, 115) and by King et al. (94) illustrate the wide range of configurations ...