向列式液晶之相位與指向矢擾動光學

Phase and Director-Fluctuation Optics of Nematic Liquid Crystals

姜哲文(Che-Wen Chiang)

指導教授 ： 楊界雄

國立交通大學/光電學院/光電系統博士學位學程/博士(2018年)

摘要

在扭轉向列模式(TN Mode)液晶顯示器中，液晶預傾角(Pretilt Angle)對顯示器畫面品質有顯著影響如: 液晶顯示器的視角、液晶顯示器的反應時間、以及將像素電極周圍的向錯線移入薄膜電晶體的黑色矩陣區域，提高TN型液晶顯示器的對比度……等。在本論文中，我們提出了一種測量TN液晶預傾角的光學方法，利用外差延遲相位量測與出平面旋轉法，測量相位差與入射角之關係，在推導TN液晶預傾角中，無須考慮混合預傾角與液晶盒厚度的莫吉恩方程式(Mauguin Equation)，因此可測得出獨立的TN液晶預傾角參數。分析實驗數據上，我們利用廣義瓊斯矩陣(Extended Johns Mateix) 描述TN液晶盒之理論模型，進而模擬相位差與入射角之關係曲線，並與實驗之曲線相互匹配，則可推算出TN液晶預傾角參數。比較現今利用出平面旋轉法量測TN液晶預傾角參數，我們相信相位差測量的方法比傳統強度測量的方法具有更簡單的量測設置、更好的穩定性、更高的信噪比和對環境電磁干擾不敏感等優點。
在本論文中，我們也研究液晶指向矢擾動對向列型液晶造成光散射之效應。理論推導上，我們擴展De Genne’s光散射方程，在光傳遞方式為e-mode或是o-mode 架構下，推導任意斜向入射光經過傾斜均勻配向(THA)液晶之指向擾動方程式。基於此擴展之方程，我們可使用出平面方法旋轉法來量測THA液晶之預傾角參數。我們的方法與Scheffer和Nehring發表的出平面方法旋轉法相比，具有設置簡單並且當液晶預傾角低於約30度時不需要復雜的數據擬合計算等優點。對於較大的預傾角的情況下，量測光穿透率與入射角(Tr-IA)曲線中找到角度極值位置，則須再減去量測空液晶盒Tr-IA曲線的結果，做為更精確的校準。

關鍵字

預傾角 ； 相位量測 ； 向列型液晶 ； 光學量測 ； 指向性擾動 ； 光散射

並列摘要

For TN LC displays, the pretilt angle of TN LC medium within the cell has a significant impact on display qualities such as viewing angles and response times as well as shifting the light leaking disclination lines into the black-matrix area within pixels of thin-film-transistor driven TN panel for high contrast ratio. In this thesis, we have developed an optical method to determine TN pretilt angle free of entanglement with TN cell gap based on heterodyne measurements of phase versus incident angle of a Gooch-Tarry-first-minimum TN cell subjected to out-of-plane rotations (OPR). We have used extended Jones matrix method to calculate the phase versus incident angle to fit the experimental results for the determination of the TN pretilt angle. Compared with published OPR methods to measure the pretilt angles of TN LC cells, our method of measuring phases has advantages of simpler in setup, better stability, higher signal-to-noise ratio, and less sensitive to ambient electro-magnetic interference than the conventional method of measuring intensity.
In this thesis, we have also investigated the light scattering due to liquid-crystal-director fluctuations (LC-DFs). We have extended De Genne’s LC-DF light-scattering equation to deal with the situations where the polarization of light propagating within a THA LC cell formed an arbitrary oblique angle with respect to the LC director within the cell. Based on the extended equations of LC-DF light scattering, we have developed an OPR method to measure the light scattering versus incident angle to determine pretilt angles of THA LC cells. Compared to the OPR method by Scheffer and Nehring, our method has the advantages of simpler in setup and no need of complicated data-fitting calculations when the pretilt angles are below about 30 degrees. For the cases of larger preilt angles, it is necessary to find the angular extremal position among the data that subtracting the measured results of a transmission-versus-incident (Tr-IA) curve of a phantom cell from that of the THA LC cell.

並列關鍵字

Pretilt angle ； Phase measurement ； Nematic liquid crystal ； Optical measurement ； Director- fluctuation ； Light scattering

參考文獻

Chapter 1

[1] C.C. Tsai, C.Chou, C.Y. Han, C.H. Hsieh, K.Y. Liao, and Y.F. Chao, “Determination of optical parameters of a twisted-nematic liquid crystal by phase-sensitive optical heterodyne interferometric ellipsometry,” Appl. Opt. 44(35), 7509 (2005).

[2] S. T. Tang and H. S. Kwok, “Transmissive liquid crystal cell parameters measurement by spectroscopic ellipsometry,” J. Appl. Phys. 89(1), 80–85 (2001).

[3] G. Baur, V. Wittwer, and D. W. Berreman, “Determination of the tilt angles at surfaces of substrates in liquid crystal cells,” Phys. Lett. 56(2), 142–144, (1976).

[4] D. W. Berreman, “Optics in Stratified and Anisotropic Media: 4×4-Matrix Formulation,” J. Opt. Soc. of Am. 62(4), 502 (1972).