臺灣博碩士論文加值系統

液晶具有雙折射的性質，而且液晶分子會受外加電場影響而指向趨於平行或垂直於電場方向。我們可以把這性質應用在改變表面電漿波發生角度以及改變波導模態上面。實驗上發現表面電漿發生角度即使在大電壓作用下變化並不大，這可用臨近金屬膜的液晶層受邊界作用力影響很大來解釋。在液晶作為夾層的層狀波導實驗，我們發現有模態分裂的情形，這可用液晶雙折射的原理模擬出來。另外，過去對於扭轉型液晶盒的穿透光在電壓開與關的瞬間會有振盪的情形，多以流動效應來解釋。但我們可給出在只考慮液晶分子原地扭轉所產生的折射率變化，便能解釋穿透光多重振盪的現象。這在實驗上也觀察的到。

In this work, we are devoted to study the optical properties of nematic liquid crystal (LC) from the anisotropic birefringence behavior view. These include the shift of minimum attenuated total reflection angle, the mode splitting, and the nonlinear dynamic oscillation. The scenario of this work will be portrayed as follows.
Attenuated total reflection (ATR) is a prominent effect in examining the excitation of surface plasmons. The Kretcshmann-Raether configuration is implemented to generate the surface plasmon and to examine the change of the refractive index of LC by an applied field. A mixture of nematic and cholesteric liquid crystal is sandwiched between two glass substrates coated with conducting films. The minimum ATR angle changes less than 1o as the applied voltage increases to as large as 30Vpp, which is controvertible to the calculation based on field induced refractive index change. This fact suggests that the orientation of LC directors adjacent to the electrode surface is unaffected in response to the external field attributing to the strong anchoring effect. Extended Jones matrix simulation imposed with multi-layered structure of LC clearly adducing this fact.
Mode splitting is found with a He-Ne laser beam reflecting through a prism-coupled liquid-crystal slab waveguide applied with an electric field. Mode splitting yields stronger manifestation as the imposed voltage passes a critical level, yet it becomes diminished above a critical high voltage. If the voltage increases even higher, mode splitting would disappear, attributing to the turning up of almost all the directors of LC to the surface. Our multi-layered matrix simulation can satisfactorily account for this phenomenon by exploiting the property of the anisotropic optical birefringence of LC under applied voltages.
Relaxation oscillations of optical transmittance after the turn-off of the applied electric field of LCs are observed when the detected light transmits through a proper adjustment of the alignment of the polarizer and analyzer. Approximated dynamic simulation, which do not concern the back-flow effect and neglect the inertia terms, of the LC molecule at each layer yields relevant polarization interference of the transmitted light. This effect can satisfactorily portray the oscillation phenomenon. Optics with the extended Jones 4x4 matrix formalism, which is relevant in elucidating the optical properties of anisotropic media, is also implemented to solve this problem.

Contents
Table Captions
Figure Captions
Chapter
1. Variation of Attenuated Total Reflection Due to the Birefringence of Liquid Crystals by the Excitation of Surface Plasmons
1.1 Introduction to Liquid Crystal……………………………………………………..1
1.2 Surface Plasmon…………………………………………………………………...3
1.3 Theory……………………………………………………………………………..4
1.4 Experiments and Simulations…………………………………………………….12
1.5 Results and Discussion…………………………………………………………...14
1.6 Conclusion ……………………………………………………………………….15
Tables ………………………………………………………………………………...16
Figures………………………………………………………………………………..18
2. Mode Splitting in the Optical Slab Waveguide Filled with Nematic Liquid Crystal
2.1 Introduction………………………………………………………………………29
2.2 Liquid Crystal Embedded Optical Slab Wave Guides…………………………...31
2.3 Theory……………………………………………………………………………31
2.4 Experiments………………………………………………………………………38
2.5 Results and Discussion…………………………………………………………...38
2.6 Conclusion………………………………………………………………………..40
Table………………………………………………………………………………….41
Figures………………………………………………………………………………..42
3. Dynamic Response in Nematic Liquid Crystal
3.1 Introduction………………………………………………………………………59
3.2 Theory……………………………………………………………………………59
3.3 Experiments………………………………………………………………………63
3.4 Results and Discussion…………………………………………………………...64
3.5 Conclusion………………………………………………………………………..66
Figures………………………………………………………………………………..67
4. Conclusions and Future Development………………………………..…………82
References……………………...……………………………………………………83
Appendix 1A: Procedures of Using the Thermal Evaporator to Evaporate the Metallic Films………………………………………………………………….86
Appendix 1B: Sample Preparation of LC Cell and Commonly used alignments for nematic LC cell………………………………………………………88
Appendix 1C: The Simulation Program for Surface Plasmons………………………90
Appendix 1D: The Fitting Program for Thin Film Parameter Using Least Square Method……………………………………………………………….92
Appendix 2A: The Simulation Program for Wave Guides…………………………...95
Appendix 2B: The Tilt Angle of Liquid Crystal on the Boundary…………………100
Appendix 3A: The Program of Measuring LC Cell’s Response in a Computer Language of GWBASIC…………………………………………....104
Appendix 3B: The Program of simulating LC director’s tilt and twist angle………107
Appendix 3C: The Program of Simulating LC Cell’s Response in a Computer Language of Mathematica…………………………………………..109

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