Novel Pretilt Angle Measurement Method for Twisted-Nematic Liquid-Crystal Cells by Apparent Retardation Measurement

Abstract

We have proposed a novel pretilt angle measurement method for twisted-nematic (TN) liquid-crystal (LC) cells. In this method, the dependence of the apparent retardation of the TN cell on the cell rotation angle is analyzed by the simple mathematic equations derived here to determine the pretilt angle and the gap. This method can be applied to the TN LC display panel. The necessary range of the cell rotation angle is from −3 • to 3 • . This provides an advantage for both constructing a compact measurement system and measuring a small-size pixel.

Simple method to obtain accurate pretilt angles for thin twisted nematic liquid-crystal cells

“…In their studies, the measured pretilt angle was only related to the extremum angle on the transmission versus incident-angle (Tr-IA) curve and the indices of refraction of the LC mixture within the cell. Similarly, there also have been many publications [3][4][5][6][7][8] on the measurements of TN pretilt angles. The published methods of measurements have been based on experimental configurations to measure the transmissions or retardations of the TN cell subjected to either in-plane or out-of-plane rotation (rotational axis either parallel or perpendicular to light-incident direction, respectively).…”

“…Therefore, the errors of the derived pretilt angle and cell gap were interdependent unless the empty cell gap was measured independently and not changed after LC injection into the TN cell. As for the out-of-plane rotation methods, Nishioka and Kurata [7] obtained data from small-angle (−3°∼ 3°) rotations and derived the pretilt angle and cell gap of a TN cell by the curve-fitting method resulting in similar uncertainties as the cases of published inplane-rotation methods. Birecki and Kahn [8] published a configuration of out-of-plane cell-rotation method to measure the pretilt angle of a TN cell.…”

P‐47: Evaluation Method of Gap and Pretilt Angle for Twisted‐Nematic Liquid‐Crystal Cells by Apparent Retardation Measurement using Two Wavelengths

“…With this aim, we have derived the Jones matrix of the TN cell rotated around the axis parallel to the cell surface and perpendicular to the ray direction as shown in Figure 1. If the azimuthal angle of the incident side director α in satisfy Equation 1, the Jones matrix of the rotated TN cell W is written approximately as Equations 2 and 3 [2].…”

“…within the range of Θ from -3° to 3°. The discrepancy in the higher Θ region is considered to be caused by uncertainty of the hypotheses employed to derive Equations 2 and 3 in this region [2]. Table I shows the comparison between the designed value and the simulated result of θ s .…”

“…We have proposed a novel method of evaluating the gap d and the pretilt angle θ s for TN cells by analyzing the dependence of the apparent retardation ∆n'd on the cell rotation angle Θ [2]. We call this method "apparent retardation measurement (ARM) method."…”