Optical Signal Processing

7

Acousto-Optic Devices

7.1.  INTRODUCTION

Spatial light modulators form the interfaces between electrical and optical systems. In Chapter 4 we described several two-dimensional spatial light modulators whose inputs are either incoherently illuminated objects or raster-scanned electrical signals. None of those modulators, however, are able to accept signals with hundreds-of-megahertz bandwidths. We therefore concentrate in this chapter on acousto-optic spatial light modulators that help to implement a wide range of processing operations on wide-bandwidth signals. These devices are key to the signal-processing architectures discussed in the remainder of this book.

7.2.  ACOUSTO-OPTIC CELL SPATIAL LIGHT MODULATORS

The advantages of optical systems, based on the use of acousto-optic cells for processing either analog or digital signals, may be summarized as a combination of high throughput, a small volume relative to competing rf systems, and low power consumption. Optical systems offer the potential for a large number of parallel channels with complete connectivity, and the high carrier frequencies (≈ 10¹⁴ Hz) allow very high channel bandwidths with little crosstalk of the type present in electronic processors. Also, optical channels have comparatively smaller power requirements, as the dissipative losses associated with electrical transmission are not present; the losses in typical optical transmission media, such as air and glass, are low.

Brillouin (75) predicted in 1922 how ...