含光學三穩態層列A型液晶之一維光子結構

Switching of Defect Modes in a One-Dimensional Photonic Structure with a Tristable Smectic-A Liquid Crystal

陳志恆(Chih-Heng Chen)

中原大學/理學院/物理研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200549

摘要

本論文成功地以水平配向之層列A型液晶藉由電壓及溫度的調控，呈現光學三穩態之特性。並將層列A型液晶引入一維光子晶體結構，利用其光學特性，展現缺陷模態多元的光強及波段的調控特性。
根據研究成果，當水平配向之層列A型液晶由垂直態鬆弛至水平態時，由於層列液晶之高秩序度，在鬆弛的過程中，層列液晶之層狀結構會與水平配向層之錨定力相互抵抗而產生散射態。而本研究確立了在層列相中，隨著溫度的改變，可經由電壓的施加及移除呈現水平、散射及垂直之三種無需電壓維持之穩態。另外，散射態的散射強度可隨施加電壓強度的改變而調控，其展現一多階段之光強調控，且其皆為穩態。將其光電特應用至一維光子晶體中，其展現多元的缺陷峰調控特性，不僅可藉由施加電壓改變液晶之有效折射率選擇波段，也可在特定波段呈現多階段的光散射調控。另外，高電壓所造成缺陷峰的過度位移，也在本論文中被討論，其原因可能為高電壓對薄玻璃造成之厚度變化所引起。綜上所述，含層列Ａ型之一維光子晶體結構，可被應用於無須使用偏光板之低耗能多頻道調控之光學元件。

關鍵字

液晶 ； 層列A型液晶 ； 一維光子晶體 ； 三穩態

並列摘要

In this thesis, a planar-aligned Smectic A liquid crystal (SmA-LC) cell which exhibits optical tristability is demonstrated by adjusting external electric field and temperature. The three stable states are planar, focal conic, and homeotropic state. Based on the switching among these states, a one-dimensional photonic crystal (PC) structure infiltrated with SmA liquid crystal as a defect layer shows memorable and tunable light-intensity and wavelength in defect modes. The optical properties of a PC/SmA-LC hybrid structure are discussed. The temperature-dependent switching mechanism of optical tristable states is further investigated in this research.
The results reveal a scattering state of smectic A liquid crystal cell led by the energy balance between anchoring and elastic energy through a relaxing process from homeotropic state to planar state. Moreover, the temperature dependent switching mechanism of optical tristable states is deeply investigated in this research. On the other hand, it is worth to mention that the scattering state shows a strong tunability of the light intensity which can retain multichannel of light scattering state without voltage-sustained. A one-dimensional photonic crystal optical device based on smectic A liquid crystal as a defect layer is used to realize a low-energy-consumption device because of the tristability of the smectic A liquid crystal. With a voltage-induced scattering state, the photonic crystal–smectic A hybrid cell can work as a polarizer-free optical switch. As a result, an electrically and thermally tunable multichannel optical device is revealed using this hybrid, optical tristable structure.

並列關鍵字

tristable ； smectic A liquid crystal ； one-dimensional photonic crystal

參考文獻

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