The function of an optically addressed spatial light modulator (SLM) is to convert the intensity distribution of an incident scene into a coherent image, or into a high brigthness incoherent image. The applications of these transducers are therefore very large since they extend, from the field of coherent optical processing and computing (Incoherent to coherent conversion) to the high resolution video image projection. A great interest is now devoted to the technological developments of these devices in several laboratories using different approaches. The basic principle of operation of an optically addressed light valve is the following. A photosensitive layer detects the incident intensity distribution and induces a charge distribution onto a material which modifies its optical properties as a function of the photoinduced voltage. Finally, the incoherent or coherent illumination beam transmitted (or reflected) by the SLM sees its amplitude or phase spatially modulated. In the last few years, the list of spatial light modulators under research and development expanded considerably.