Real time correlator with liquid crystal panels:: modulation optimization

In the last years, some optical pattern recognition techniques have been developed based in real time correlators using spatial light modulators (SLM). In this work, the building of a real time convergent optical correlator is presented. In the correlator, both the input scene and the filter are implemented using twisted nematic liquid crystal display panels (LCD) as spatial light modulators. The modulation of this kind of panels is generally coupled phase and amplitude modulation for linearly polarized states. So, elliptically polarized light configurations have been used to optimize the LCD response and to perform either phase only or amplitude only modulation. Linear polarizers and wave plates are combined at the input and the output sides of the LCD to obtain these configurations. The input scene is represented in either an amplitude only or in a phase only SLM. The filter has been represented in a phase only SLM. Some experimental results obtained with the built correlator are shown.