光彈調變式偏光儀對光學補償彎曲式液晶盒的量測

Abstract

本論文研究量測OCB液晶盒的預傾角，藉由量測OCB液晶盒在各入射角的相位延遲與理論曲線擬合以求出最佳預傾角大小，同時修正液晶盒在注入液晶之後的厚度。OCB液晶盒的液晶分子排列狀態在外加電壓加至臨界電壓的情況下由斜展態而成彎曲態。當OCB液晶盒在彎曲態時突然移除偏壓，會有一短暫且高亮度的暫穩態，稱為鬆弛彎曲態，因不需要保持臨界電壓，故有省電的優點。利用光彈調變式偏光儀量測OCB液晶盒在外加驅動電壓的偏光參數Ψ和Δ，並將其轉換成史托克參數，除了可以觀察OCB液晶盒的出射光偏極態變化外也可轉換成穿透率，並將其繪於邦加球上以觀察其動態軌跡。我們也利用不同驅動電壓下比較OCB液晶盒在亮暗態操作的亮度和對比度，藉以瞭解在暫穩態操作的省電機制。

This work measured the pretilt angle of the OCB cell by photoelasitc modulated polarimetry. We measured the phase retardation at different incident angles then fitted them with that deduced by the theoretical formula for finding the best pretilt angle and the cell gap after the cell filled with the liquid crystals. The structures of the OCB cell under applied voltage had three kinds of states: splay state, bend state and twist state. A metastable state does exist when one suddenly removes the driving voltage, but its transmittance is high, this state is also named as relaxed bend state. This state can reduce the power consumption because no critical voltage is required for the switching. The photoelasitc modulated polarimetry measured the ellipsometric parameters Ψ and Δ of the OCB cell under various driving voltage. The Stokes parameters can be deduced by the measured Ψ and Δ, then we traced out these polarization states on Poincaré Sphere in this work. Finally, we compared the brightness and the contrast ratio when the OCB cell operated in the relaxed bend state and the bend state.