Multiple image control with an 8-bit frame grabber. Use in a VanderLugt correlator

The reduction of geometrical distances in optical correlators, in order to build miniaturized systems, has become a necessityfor realistic applications [1]. In general, the scope of the studies carried out is only focused in some parts of the problem.Nowadays, liquid crystal devices (LCD), usually removed from commercial videoprojectors, are used to display images inoptical setups. As a result of using pixelated panels, the viability study of building an optical correlator in a reduced spaceshould not be only limited to a design of optical systems. It must include an analysis of the behaviour of the displayingdevices. Another issue that has not been raised yet is the reduction of the material needed to control simultaneously twoLCDs in a Vander Lugt correlator, which involves a duplication in the driving electronics.We analyze in depth several engineering problems regarding the construction of a Vander Lugt correlator with LCDs at theinput and Fourier planes. In order to reduce the length of the setup we have designed two telephoto systems. An originalmethod to control both devices with a single 8-bit frame grabber and a single videoprojector electronics is presented. We havesolved the problems related to pixel-by-pixel control when displaying the data from the frame grabber on the LCDs. Anaccurate analysis of the phase modulation capability of the panels is also discussed. Experimental results obtained with thissetup are presented