利用固化電壓減少垂直排列高分子穩定型液晶之散射效應

Reduction of the Scattering Effect of Vertically Aligned Polymer Stabilized Liquid Crystal by Curing Voltage

李彥民(Yan-Min Li)

指導教授 ： 蔡永傑

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.00118

摘要

液晶科技的應用已經廣泛地運用在我們生活周遭，並不再局限於顯示器中，還有許多方面可以被應用，例如我們會討論的法布立－培若干涉儀(Fabry-Perot interferometer)可以做成可調變波長濾波器(WDM)內部的元件。對於一般液晶分子的特性，在轉換不同電壓之間液晶分子會改變不同排列方式，所需要花費的時間稱之為響應時間(Response Time)，這對顯示器來說是很重要的參數，響應的時間必須小於人類肉眼視覺停留時間，眼睛才會感覺顯示器的畫面是呈現連續的狀態。最近有許多高分子穩定型液晶(Polymer Stabilized Liquid Crystal, PSLC) 的研究不斷的被發表，它是經由液晶與單體以特定比例下組合而成的混和物，當PSLC經過紫外光固化後單體會變成聚合物，使液晶分子在降電壓過程中加速回復到原本沒有加電壓的排列狀態，故放電壓響應時間toff會縮短，另外加電壓響應時間ton可經由過驅電壓(overdrive voltage)去改善。
高分子穩定型液晶常見的現象是加上超過臨界點的電壓時，因為聚合物的結構無法使液晶有規律地旋轉倒向，使液晶分子會隨機地倒向造成明顯的散射現象，加上如上述說明高分子穩定型液晶具有快速的響應時間，PSLC可以被做成光學儀器中的快速門閘(shutter)和電控調光玻璃(privacy glass)。我們的研究方向是利用它快速響應時間的優點在法布立－培若(Fabry-Perot)干涉儀中以達到快速可調變波長濾波器，並加上固化電壓可以改變垂直排列高分子穩定型液晶的散射特性，讓它在加上電壓後仍然保持高穿透率去調製波長，這種濾波器在通訊系統中有著快速調變波長的功能，是被看好的。

關鍵字

法布立－培若干涉儀 ； 高分子穩定型液晶 ； 液晶 ； 可調變波長濾波器 ； 固化電壓

並列摘要

Liquid crystal technologies have been used in our daily life. It has not only been utilized in displays but also in other applications such as Fabry-Perot interferometers in wavelength division multiplexing (WDM). Liquid crystal has a characteristic that it would change its molecular orientation when a voltage is applied. The time it takes to rotate is called response time. For display and many other applications, this is a very important parameter. For example, the display images would appear as a continuous motion for human visual system if response time is smaller than time interval that can be distinguished by human eyes. Due to its fast response time, it can also be used as rapid shutters for optical instruments or used as privacy glass.
Polymer Stabilized Liquid Crystal (PSLC) is one kind of liquid crystal (LC) gel that has been reported. It is composed of liquid crystal and monomer under certain ratio. After UV curing, monomers would become polymers which can help LC molecules restore back to original state more quickly when a lower voltage is applied. Hence, the LC decay time can be shortened. On the other hand, the rise time can be improved by applying an overdrive voltage. PSLC usually has a common phenomenon which is that, after an applied voltage, the LC molecules would tilt randomly which causes strong scattering. This is due to the structure of the formed polymer which does not allow LC molecules to tilt consistently. In this thesis, a curing voltage was found to be able to help reduce the strong scattering effect of the VA-PSLC (Vertical Alignment PSLC) significantly. It therefore can have a high on-state transmittance. We take the advantage of fast response time of PSLC and place it inside a Fabry-Perot cavity to achieve a wavelength tunable filter. These filters can have potential applications in wavelength tuning applications (e.g. WDM) in telecommunication systems where high speed is desirable.

並列關鍵字

polymer stabilized liquid crystal (PSLC) ； Liquid Crystal ； curing voltage ； Fabry-Perot filter ； wavelength tuning

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