電調變液晶波導; Electrically Tunable Liquid Crystal Waveguides

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题名:	電調變液晶波導;Electrically Tunable Liquid Crystal Waveguides
作者:	粘珊綺;Shan-Chi Nien
贡献者:	光電科學研究所
关键词:	液晶;中空光波導;電調變;liquid crystal;hollow waveguides;electrooptic effect
日期:	2010-07-19
上传时间:	2010-12-08 14:20:59 (UTC+8)
出版者:	國立中央大學
摘要:	本論文主要是在中空光波導中灌注液晶E7形成液晶核心光波導，由於液晶分子的排列情形會受外加電場的影響而改變，利用此種可調變的特性與波導作結合，期望將波導變為可調變的元件。本文所使用的液晶波導膜層結構有兩種，一種為SiO2膜層，另一種為運用非晶相矽與氮化矽兩種材料所組成的多層膜結構即布拉格反射鏡，其分別利用全反射與干涉原理將光侷限於液晶波導中，操作波段皆為1550 nm。在膜層設計上，我們利用傳遞矩陣法決定膜層結構之後，再藉由光束傳播法(Beam Propagation Method)模擬計算液晶波導的侷限效果，由模擬的結果得知：SiO2膜層波導無論在TE或TM模態下都具有良好的侷限效果，而多層膜結構波導在TM模態下當液晶核心折射率為no時侷限效果較ne好，因此期望利用此結果達到調變的作用。在量測方面，無論入射何種偏振光，SiO2膜層波導輸出端的強度隨著外加電壓的上升而減弱，當外加電壓為4~5VPP時，輸出端的強度最弱其衰減強度達到30dB，可應用於光開關。藉由量測各個電壓下液晶波導的穆勒矩陣(Mueller matrix)並對矩陣作極化分析，幫助我們了解液晶波導的極化特性。而在多層膜結構波導方面，由於波導的耦合損耗與對TM模態的侷限效果較為不佳，因此結果不如預期。 In this study, we fabricate the liquid crystal waveguides by infiltrating liquid crystal E7 into hollow waveguides (HWGs). The reorientation of the high susceptibility of liquid crystals (LCs) molecular is achieved by applying the external fields to change the optical characterization of the liquid crystal waveguides. We fabricate two types cladding structures of liquid crystal waveguides. By using the total internal reflection (ITR), the first structure is based on the waveguide in which the cladding layer is SiO2 layer. In the second structure, the cladding layer is amorphous silicon/silicon nitride (Si/Si3N4) multilayer. The wavelength of the launched light into the waveguides is 1550nm. We design the cladding structures and the light propagation in liquid crystal waveguides by the transfer matrix method and by beam propagation method, respectively. The simulation results show that the SiO2-cladded waveguide provides a good confinement for the TE and TM modes. The waveguides with multilayer provide better confinement for the refractive indices of LCs no than the refractive indices ne. By applying external voltage to the SiO2-cladded waveguide, the output intensity decreases with voltage. This phenomenon is polarization-independent. The devices can serve as an electrically tunable liquid crystal switch with over 30dB attenuation at 4~5Vpp. Moreover, we also measure the Mueller matrices of SiO2-cladded waveguide under different voltages to understand the polarization properties.
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