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In Chapter 28, we showed that the theoretical communication techniques that are so common in electrical engineering are also very useful in optics because of the linear, spatially invariant nature of many optical systems. In a similar manner, the concept of modulating signals on unique carriers, which is a common technique in radio and television, has also found its way into optics in the form of modulated imagery and holography. We have already seen that the image is retrieved from the hologram by looking in the angular direction, which was unique to the holographic reference beam. In fact, different images have been stored and retrieved from a single hologram by using different carrier frequencies and/ˆ•or recording distances. In this chapter, we discuss storage and retrieval by carrier-modulated imaging techniques. In this process, different images are stored on a single medium (film) with unique carriers and retrieved by tuning the retrieval system to the specific carrier of interest. Different implementations of the concept are given and the capability of carrier-modulated imagery is demonstrated.
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