An nMOS addressed liquid crystal spatial light modulator
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Coherent optical data processing is recognised, for many applications, as a viable alternative to digital electronic signal processing; the case for using coherent optics is particularly strong when the data to be processed is two dimensional in nature. It has long been accpeted that, in order for coherent optical processing to achieve its full performance potential, two dimensional spatial light modulators - capable of operating in real time - are essential at both the object plane (where the data is input to the system) and the Fourier plane (where the operation carried out on the data is determined). Most previous research in the field of spatial modulators has concentrated on optically addressed devices for use in the object plane. This thesis describes a prototype liquid crystal over silicon spatial light modulator built to test the feasibility of using such devices in a coherent optical processor. Optically, the device operates as a binary amplitude modulator, consisting of a square array of 16x16 pixels, each of size 100x100 m^2 and located at 200m centres. The integrated circuit is designed for a 6m wafer fabrication process. Each pixel of the IC contains a static memory element (which stores a digital logic voltage corresponding to the optical state of that pixel) and provides a stable square wave voltage signal to drive the liquid crystal layer. The component parts of the spatial light modulator are tested individually: the liquid crystal, in test cells, for contrast and switching speed; the IC for electrical performance and optical (flatness) characteristics. The effect of pixellation on optical performance is investigated. The performance of live devices is demonstrated. The results indicate the feasibility of using such a device as a binary amplitude spatial light modulator.