兆赫波光電子學因為在生物醫學、光譜學等應用的驚人前例,已成為光電產業一個不斷成長的領域,在各式應用中,偏極的相依性往往限制了其應用的彈性。 本篇論文中,我們嘗試利用膽固醇型液晶的在兆赫波段無偏振依存的特性,探討它在兆赫波光電子學的可能應用。
首先,我們示範了利用電控液晶來製作相位調變量可超過 2π 且調變速度達到 0.5sec 的相移器,這是首次將速度加速至低於秒級的兆赫波相位調變器,並討論了在過程中發現的因厚度與施加電壓過大而導致 optical bounce 的現象,並給出當施加電壓到達一臨界點時,反應速度便與厚度 直接相關的結論。
此外,我們也開發了一偏極獨立的兆赫波段電控可調式帶通濾 波器,半高寬(FWHM)約為11GHz,截止帶(stop band)從 367GHz 到 452GHz,品 質因子(Quality factor)約為 38,調變範圍為 14GHz,並討論它在即時光譜儀等應用的可能性。

In recent years, terahertz (THz) photonics have attracted plenty of attraction due to its remarkable progress. As its potential in the field of communication, spectrum analysis and so on, the demand of high performance quasi-optic components such as phase shifters, band pass filters or polarizers is strongly increasing. However, these devices need polarizer or other polarization control system to achieve polarization independency.
The first part of this thesis, polarization independent electrical controlled 2p THz phase shifter with sub-second modulation speed was demonstrated by using cholesteric liquid crystal (CLC). The device was constructed by stacking three CLC layers. Each CLC layer with thickness of 1.5mm was sandwiched by two fused silica glasses coated with ITO for electrode. The CLC was made by chiral dopant mixed in a nematic liquid crystal (NLC) host BL006 and pitch length is around 20μm. The structure of CLCs became visible homeotropic texture from invisible focal conic texture when the driving voltage increases from zero till over 360V. The modulation speed increases as the driving voltage increasing. The response time up to 500 ms was successfully achieved using the multi-layer structure. The polarization independence of this component was performed about l/60. Feasibility of 100ms modulation speed was discussed as well.
Second, we demonstrated a polarization independent tunable THz band pass filter based on one-dimensional photonic crystal cavity and using CLC. The CLC layer, made by chiral dopant mixed in a nematic liquid crystal (NLC) host BL006 with around 20μm pitch length, was sandwiched by two Bragg mirror with half-wavelength optical thickness of 650μm. The THz Fabry-Perot(FP) is demonstrated using two three-pairs THz high reflective structures. The stop band of 85GHz and 3dB bandwidth of 11GHz are demonstrated. The corresponding Q-factor is about 38. By filling with CLC in the THz FP, the frequency can be tuned from 406GHz to 420GHz as applying voltage on CLC cell. This is the first time to our best knowledge that the electrical controlled THz narrow-band-pass is polarization independent and with tuning rang of 14GHz.

中文論文審定書 I
英文論文審定書 II
致謝 III
摘要 V
Abstract VI
目錄 VIII
圖次 X
表次 XIII
第一章 緒論 1
第二章 兆赫波系統理論與液晶簡介 6
2.1 光導天線輻射機制介紹 8
2.2 電光晶體取樣法 11
2.3 兆赫波時域解析光譜系統 16
2.4 液晶簡介 19
2.4.1液晶介紹 19
2.4.2 液晶分類 19
2.5 液晶的物理特性 22
2.5.1 秩序參數 22
2.5.2 光學異向性 22
2.5.3 介電異向性 24
2.5.4 液晶的連續彈性理論 25
第三章 兆赫波段下偏極獨立的高速電控相位調變器 27
3.1兆赫波段下相位調變方式介紹 29
3.1.1 磁控向列型液晶兆赫波相位調變器 29
3.1.2 電控向列型液晶兆赫波相位調變器 31
3.2 膽固醇型液晶與反應時間量測介紹 34
3.2.1 膽固醇型液晶介紹 34
3.2.2 反應時間量測介紹 40
3.3 不同結構對相位調變反應時間的影響 44
3.4 驅動電壓下液晶反應時間shooting現象的討論 50
3.5 偏振獨立性的2π相位調變器 55
3.6 結論 58
第四章 偏極獨立的兆赫波帶通濾波器 59
4.1 四分之一波長multilayer與Fabry-Perot 共振腔簡介 60
4.1.1 四分之一波長multilayer 簡介 60
4.1.2 Fabry-Perot 共振腔簡介 62
4.2 週期性堆疊結構構成之布拉格反射鏡DBR模擬 67
4.3 兆赫波段下可調式帶通濾波器 69
4.3.1 帶通濾波器 69
4.3.2 電控可調帶通濾波器 73
4.4 偏振獨立的兆赫波段可調式帶通濾波器 75
4.5 結論 76
第五章 總結與未來展望 77
5.1 總結 77
5.2 未來展望 78
參考文獻 79

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