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

Abstract

Modern thin-film-transistor-driven twisted nematic (TN) products on the market require thin cell gaps below the value to satisfy the condition of the Gooch-Tarry first minimum in transmission for fast response times and wide viewing angles. For the first time to our knowledge, we have developed a simple experimental method based on a new configuration of out-of-plane cell rotation and analyzed our data by extended Jones matrix method to obtain accurate pretilt angles for such thin TN cells where the well-accepted configuration of the out-of-plane cell rotation method analyzed by Birecki and Kahn [The Physics and Chemistry of Liquid Crystal Devices (1980), p. 115] was insufficient to address.

P‐106: Pretilt Angles and Liquid‐Crystal Director‐Deformation Profiles of Inverse Twisted Nematic Liquid Crystal Cells

“…We used a configuration of out-of-plane cell rotation method shown in Fig. 1 for the simulations [8,9] and measurements of the phase retardation versus incidence angle (Ph-I.A.) curves of ITN and ATH cells.…”

Entanglement-free determination of pretilt angles of twisted nematic liquid-crystal cells by phase measurement

“…For TFT-TN products, the first-minimum cell gap is essential to having fast response times and wide viewing angles. In 2013, Wang and Yang [9] published a paper by using intensity measurements based on a new configuration of the OPR method and analyzed data by extended the Jones matrix method to obtain accurate pretilt angles for thin (first-minimum) TN cells, avoiding the entanglements of cell gap and pretilt angle measured by the IPR methods.…”

“…In this Letter, we have replaced the intensity measurements by phase measurements in a similar OPR method [9] to determine the pretilt angles of thin TN cells. We show that the analyses using the extended Jones matrix to calculate the phase versus OPR angle to fit the corresponding experimental results to determine the TN pretilt angle are much simpler than analyzing the measured intensities.…”

“…In our phase measurements, we have used heterodyne mixing of two laser beams from a Zeeman laser system [10] . We believe that our method of measuring phases has the advantages of a simpler setup, better stability, simpler calculations, and less sensitivity to ambient electromagnetic interference (EMI) than the published method of measuring intensities [9] .…”

“…Wang and Yang [9] published intensity measurements to determine pretilt angles of thin TN cells. Three different OPR schemes used to derive pretilt angles of the thin TN Table 2 for comparison.…”