Simple technique for determining the extraordinary axis direction for twisted-nematic liquid-crystal spatial light modulators

We report a simple technique for determining the orientation of the extraordinary axis at the input side of a twisted- nematic liquid crystal spatial light modulator. In this approach, we illuminate the display with linearly polarized light and examine the diffraction pattern as we change the external voltage applied to the display. When the incident light is polarized along the extraordinary axis, we see changes in the diffraction pattern as a function of applied voltage. Experimental measurements and theory are presented.