Before proceeding to a discussion of particular SLMs, it is worth summarizing their salient parameters (Table 8.1), which were discussed in Sect.2.3. Note that in some specific applications the requirements on SLM parameters may lie beyond the ranges indicated here, because we give values for the sake of reference. However, if a real device has a set of parameters inferior to the lowest values, the extent of its applicability will be restricted first of all because the optical information processing system using such an SLM will be unable to compete with the electronic processing units. We notice also that the list is not complete, since it does not include such parameters of practical significance as cost, reliability, energy consumption, and ease of handling, which may be deciding factors in the choice of a modulator. Besides the photorefractive SLMs, we shall consider the Titus and Phototitus devices that use electro-optic crystals. The readout light is modulated in these SLMs through the electro-optic effect, image recording occurs due to nonuniform charge accumulation. These devices can, therefore, be analyzed in the framework common to all SLMs discussed in this monograph.