擴增實境(Augmented reality, AR)顯示器能將虛擬的數位影像與現實世界相結合，被視為下一世代的顯示技術。AR顯示器主要包括光機(Light engines)和合光器(Optical combiner)。為了讓使用者享受優良的視覺效果，同時保持頭戴式裝置的輕薄，合光器在其中扮演了關鍵角色。傳統的分光器式、自由曲面式或反射型波導的合光器雖能擴大視野，但會導致元件體積增加和影像扭曲。因此，繞射型波導合光器，使用光柵作為耦合器，成為重要的開發方向。光柵製成的繞射元件廣泛應用於繞射型波導技術中，能有效增加視野並縮小元件體積。使用上，繞射光柵需要具備較大的繞射角度，以滿足全內反射的臨界角度，同時還需高繞射效率和寬光譜頻寬，以提高傳播效率和成像品質。常見的繞射型波導合光器根據繞射元件的不同可以分為表面浮雕光柵(Surface Relief Gratings, SRGs)、體積全像光柵(Volume Holographic Gratings, VHGs)和偏振體積光柵(Polarization Volume Gratings, PVGs)。其中，偏振體積光柵因其高繞射效率、大繞射角度、偏振選擇性、低製造成本和寬響應帶寬等特性而廣受關注。
本研究將開發液晶偏振體積光柵，並將其作為繞射型波導合光器應用於AR顯示技術中。在偏振體積光柵元件的製作與使用上，可分為主動式和被動式元件。第一部分使用兩道具有正交圓偏振光的雙光干涉雷射曝光系統，在光配向層上寫入具有週期性線偏振的配向圖案，並使用全聚合物型膽固醇液晶材料製作PVG薄膜元件。透過調整曝光時兩道圓偏振光之間的角度，製作出滿足全內反射臨界角度的PVG元件。完成的PVG元件將作為繞射型波導系統的輸入和輸出端，並與波導板結合，形成合光器的光學系統，為被動式繞射型波導系統，並探討優化成像品質及減少損耗的相關參數。
除了上述被動式繞射型波導系統外，若將輸入或輸出端替換成主動式元件，則可為AR顯示器系統提供更多應用。因此，第二部分研究主動式PVG元件，使用雙光干涉系統對光配向層進行曝光後，利用聚合物穩固型膽固醇液晶製作PVG，取代第一部分的被動式元件作為輸入耦合端，通過施加電場使液晶解旋，消除週期性的折射率變化，使PVG在此狀態下不具繞射效果，作為光開關使用。
最後，除了作為光開關的調製器外，能切換反射和穿透的主動式PVG元件也具發展潛力。本研究將利用電流體效應，施加低頻電壓使CLC螺旋軸垂直配向方向排列，形成週期性橫向螺旋態(Uniform lying helix, ULH)，利用其單光軸晶體的特性，作為穿透式元件使用，達到可電控切換反射(Planar)和穿透(ULH)的主動式PVG元件。

Augmented reality (AR) displays can integrate virtual digital images with the real world and are considered the next generation of display technology. AR display devices mainly consist of light engines and optical combiners. To provide users with an excellent visual experience while maintaining a lightweight head-mounted device, the optical combiner plays a crucial role. Traditional optical combiners, such as beam splitters, freeform surfaces, or reflective waveguides, can enhance the field of view. However, they frequently result in increased component size and image distortion. Consequently, diffractive waveguide combiners, which employ gratings as couplers, have emerged as a significant area of development. Gratings utilized in diffractive elements are extensively employed in diffractive waveguide technology, as they are capable of effectively expanding the field of view and reducing component size. For practical applications, diffractive gratings must exhibit a large diffraction angle to meet the critical angle for total internal reflection, in addition to high diffraction efficiency and broad spectral bandwidth to enhance transmission efficiency and imaging quality. Common diffractive waveguide combiners can be categorized based on the type of diffractive elements used: surface relief gratings (SRGs), volume holographic gratings (VHGs), and polarization volume gratings (PVGs). Among these, PVGs are highly regarded for their high diffraction efficiency, large diffraction angles, polarization selectivity, low manufacturing cost, and broad response bandwidth.
This study aims to develop liquid crystal PVGs and apply them as diffractive waveguide combiners in AR display technology. The fabrication and application of PVG elements can be divided into active and passive components. In the first part, a two-beam interference laser exposure system with orthogonal circularly polarized light is employed to create periodic linear polarization alignment patterns onto the alignment layer. The fully polymerized cholesteric liquid crystal (CLC) materials are employed in the fabrication of PVG film elements. By adjusting the angle between the two circularly polarized beams during exposure, it is possible to produce PVG elements that meet the critical angle for total internal reflection. The completed PVG elements are subsequently utilized as input and output couplers in the diffractive waveguide system, in conjunction with waveguide plates to form the optical system of the combiner, thereby constituting a passive diffractive waveguide system. Furthermore, relevant parameters are investigated to optimize imaging quality and reduce loss.
Beyond the passive diffractive waveguide system made from fully polymerized cholesteric liquid crystals, replacing the input or output couplers with active components can provide more applications for the AR display system. Therefore, the second part of the study focuses on active PVG elements. After exposing the alignment layer using a two-beam interference system, polymer-stabilized cholesteric liquid crystals (PSCLCs) are used to create PVGs. These replace the passive elements from the first part as input couplers. By applying an electric field to unwind the liquid crystal helices, the periodic refractive index change is eliminated, making the PVG non-diffractive in this state and acting as an optical switch.
Finally, in addition to its use as an optical switching modulator, active PVG elements capable of switching between reflective and transmissive states are also promising. In this section, the electrohydrodynamic effect in CLCs is exploited by applying a low-frequency voltage to align the CLC helix axis perpendicular to the alignment direction to form a uniform lying helix (ULH) state. This state, which exhibits uniaxial crystal properties, can be used as a transmissive element to achieve electrically controllable switching between reflective (planar) and transmissive (ULH) states in active PVG elements.

中文審定書 i
致謝 ii
摘要 iv
Abstract vi
目錄 ix
圖目錄 xii
表目錄 xviii
第一章 緒論 1
1-1 研究背景 1
1-2 研究動機 7
第二章 液晶偏振光柵 8
2-1　液晶的種類及物理性質 8
2-1.1液晶的定義及種類 8
2-1.2液晶物理性質 13
2-2　貝里相位(Pancharatnam-Berry phase) 17
2-3　偏振光柵的結構及光學性質 19
2-4　偏振光柵的製作 26
2-4.1光配向機制 26
2-4.2曝光架設系統 28
第三章 近眼顯示器 34
3-1　基於PVGs的波導顯示結構及原理 34
3-2　參數定義 36
3-3　繞射型波導 38
3-3.1被動式波導系統 38
3-3.2主動式波導系統 43
3-3.3繞射型波導系統的挑戰 45
第四章 量測結果與分析 47
4-1　材料介紹及比例 47
4-1.1材料種類 47
4-1.2材料比例 53
4-2　樣品製作 55
4-3　曝光系統 57
4-4　量測系統 59
第五章 實驗結果與討論 62
5-1　聚合條件探討 62
5-1.1液晶溶液濃度 62
5-1.2有/無氮氣環境 64
5-1.3聚合光強度之影響 68
5-2　不同入射角度耦光 69
5-3　不同波導板厚度對耦光影響 72
5-4　不同輸出端厚度對耦光影響 78
5-5　繞射型波導系統實際投影效果 80
5-6　主動式元件用於輸入耦合端 82
5-6.1基於膽固醇液晶的主動式元件 82
5-6.2添加聚合物單體 85
第六章 可切換式半反穿偏振光柵元件 88
6-1　前言 88
6-2　文獻回顧 89
6-2.1半反穿PB相位元件 89
6-2.2 ULH態的驅動方式 92
6-3　研究動機 94
6-4　實驗製程 95
6-5　電控驅動方式 96
6-6　結果與討論 97
6-6.1不同液晶盒厚度 97
6-6.2不同PG週期 98
6-6.3繞射效率量測 99
6-6.4實際元件效果呈現 101
第七章 結論與未來工作 103
7-1　結論 103
7-1.1繞射波導顯示系統 103
7-1.2可切換式半反穿偏振光柵元件 104
7-2　未來規劃 105
參考文獻 106

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