Simultaneous measurement of twist angle and cell gap of a twisted‐nematic cell by an optical method

Abstract— An optical method is presented which allows one to measure simultaneously the twist angle and cell gap of a filled twisted‐nematic liquid‐crystal display (TN‐LCD) that has an arbitrary unknown twist angle between 0 and 360°. It can also determine the sense of handedness of the twist and the two rubbing directions of an unknown panel. Using this method, the measurement uncertainty of the cell gap is within 1% and the measurement uncertainties of the twist angle and rubbing directions are within 1°. 1993 Society for Information Display