含扭轉向列液晶之一維光子晶體的光譜模擬

Modeling and simulation of a one-dimensional photonic crystal with a twisted nematic defect layer

艾倫(Aaron Archibald)

中原大學/理學院/奈米科技碩士學位學程/碩士(2012年)

https://doi.org/10.6840/cycu201200466

摘要

液晶為一種介於液態及固態的物質，其排列方式除了具方向秩
序度外，亦可類似固態物質同時具有方向及位置秩序度。由於液晶為
異方性物質，在各個方向的物理特性皆不同，根據其介電異方性，可
藉外加電壓改變液晶分子的指向，又，由於其光學上的異方性，當光
線經過液晶時，光的偏振態會隨入射的方向有所改變。而液晶分子的
排列可利用高分子配向層給予液晶分子在邊界區塊的錨定束縛力。利
用上述之基本特性，液晶在現今的顯示器市場上被廣泛的應用。由於
液晶顯示器上的應用開發已相當完善且成熟，導致研究人員針對此多
元化的物質，研究其他應用的可能性。
本研究之結果將應用在未來的液晶技術中，其探索在扭曲向列
裡之可調控一維光子晶體缺陷層中，所配置使用的液晶材料；一維光
子晶體結構是由兩個介電材料交替層堆疊而成之，故每個光子晶體結
構之介面所反射而得之干涉條紋，與裝置的每一層的厚度和折射率息
息相關；所以上述之參數設計與整體傳輸於多層結構中相互應。本研
究在液晶層結構中，提供裝置調整光譜特性的方法並使欲傳播之光產
生偏振旋轉，並將此方法應用在混合光子晶體/液晶設備，其光的偏
振和強度的調控極為引人側目，故此研究將在新液晶材料之應用帶來
新的一道曙光。
一維光子晶體中，扭轉向列缺陷層的許多構造尚未被發現。扭
轉向列結構發展利用相同的方法被應用在顯示器上，這種扭轉向列結
構在光子晶體中是必須被發現，本研究開發的模型計算對於光穿透等
向材料層，像光子晶體結構、以及扭轉向列層，經通過複合裝置可被
模擬預測，藉由計算各材料層的厚度和擬合每個部份的穿透曲線來塑
造穿透裝置每個部份，結果證明這項技術可以準確的預測來估算光子
晶體結構中液晶層的厚度，針對光穿透光子晶體/扭曲向列裝置的扭
曲角與置入時的極化，從測試樣品中收集數據並論證其一系列光子晶
體/扭曲向列計畫的光學性質。結果得知，模擬的數據與實驗數據相
吻合且其裝置可作為波長選擇器、過濾器、強度調控器。

關鍵字

扭轉向列型液晶 ； 一維光子晶體 ； 光譜模擬

並列摘要

Liquid crystals flow like liquids yet possess either or both positional
and orientational order, such as a solid crystalline material would. They
exhibit both dielectric anisotropy, allowing their orientation to be
controlled by an applied external field, and optical anisotropy, allowing
them to change the polarization of light transmitting through them. Many
stable organizations of liquid-crystal (LC) molecules are realized with the
assistance of polymer alignment layers, anchoring the orientation of LC
molecules at the domain boundaries. These properties are utilized to
create high quality LC displays widely available in the market today.
However, the development and application of LC materials for display
devices is a well-established and maturing field, leading researchers to
investigate other possible applications of this versatile state of matter.
This work is a result of the ongoing search for tomorrow’s LC
technology, exploring the use of a LC material in a twisted-nematic (TN)
configuration as a field-controllable defect layer within a onedimensional
(1D) photonic crystal (PC). The 1D PC structure is a stack of
alternating layers of two dielectric materials. Reflections at each interface
of the PC structure create interference patterns based on the thickness and
refractive index of each layer of the device. These parameters are
designed accordingly to yield a desired overall transmission through the
multilayer structure. The inclusion of a LC layer adds new functionality
to this structure, providing a method for tuning the spectral properties of
the device and contributing an ability to rotate the polarization ofpropagating light. These new features of the hybrid PC/LC device are
attractive for application where control of the intensity or polarization of
light is required, opening the door for a possible new application of LC
materials.
Many configurations of a twisted-nematic (TN) defect layer within a
1D PC are yet unexplored. In the same way the TN configuration
developed over time for display application, the twisted-nematic layer
within a PC must be investigated. This study develops models for
calculating the transmission of light through layered isotropic materials,
such as the PC structure, as well as through the TN layer. The
transmission through the composite device may then be predicted though
simulation. The transmission of each component of the device is modeled
by calculating the thickness of each material layer, fitting the
transmission curve of each component. It is shown that this technique can
be used to estimate the thickness of the LC layer within the PC structure
as well as provide accurate predictions for the transmission of light
through a hybrid PC/TN device having arbitrary twist angle and input
polarization. Further experimental data collected from test cells
demonstrate the optical properties of several PC/TN schemes. It is found
that simulation results closely match experimentally obtained data, and
the devices may serve well as wavelength selectors, filters or intensity
modulators.

並列關鍵字

one-dimensional photonic crystal ； simulation ； twisted nematic liquid crystal

參考文獻

[1] E. Yablonovitch, “Inhibited spontaneous emission in solid-state

physics and electronics,” Physical Review Letters 58(20),

Bartl, “Discovery of a diamond-based photonic crystal structure in

[3] W. D. Callister, Materials Science and Engineering: An Introduction,

(John Wiley & Sons, Hoboken, 2006).