Study of the modulation capabilities of parallel aligned liquid crystal on silicon displays

Among the existent technologies of spatial light modulator devices, parallel aligned liquid crystal on silicon displays (PA-LCoS) have found wide acceptance. They are especially interesting since they provide phase-only modulation with no coupling of amplitude modulation. Optimal use of these devices requires proper calibration of their modulation capabilities in order to minimize some degradation effects found in the literature, such as flicker or anamorphic and frequency dependent modulation. In this work we apply calibration techniques developed in our lab, basically the classical linear polarimeter adapted to be able to take into account the existence of flicker. This method enables to obtain both the average retardance and a good estimation of the magnitude of the phase fluctuation when flicker is present. Various addressing formats are discussed and variations in the magnitude of the applied voltages are considered in order to amplify the retardance dynamic range and to enhance linearity in the device. Finally, two electrical configurations intended for phase-only and amplitude-mostly modulation regimes, useful e.g. in diffractive optics, are given.