本研究旨在針對傾斜螺旋態結構(Heliconical structure)於施加相對較高的電場下，反射如藍光等較短波長的波段時，其折射率差(∆n)明顯下降，造成反射頻寬變窄與反射率下降之問題。本研究透過摻雜液晶聚合物並利用電場調控及照光聚合，提出雙段式聚合法，實現低電壓驅動、反射帶中心波長可控性高與寬頻反射之可調式光學濾光元件。實驗材料採用正型液晶5CB為基底，搭配液晶二聚體CB7CB、CB11CB及手性分子S811以形成傾斜螺旋態結構，並加入液晶聚合物RM257與光起始劑DMPAP進行紫外光照光聚合。首先以單段聚合觀測在傾斜螺旋態結構下進行照光固化會造成螺距縮短與錐角變化，導致中心反射波長藍移與頻譜拓寬，然而此方法同時伴隨反射率下降與波長偏移不可預測之問題。為克服此限制，進一步提出雙段式聚合法，於第一段照光產生非均勻分佈之螺距與錐角，進而使頻寬增加，再於第二段施加目標電壓條件下進行結構固化。實驗結果顯示，雙段聚合可在保持高反射率與可控中心波長之下，將頻譜穩定拓寬，同時操作電壓明顯降低。透過貝里曼矩陣模擬證實，頻譜拓寬主因為螺距與錐角於厚度方向上的非均勻分佈，亦可藉由模擬參數反推出結構演變機制。本研究不僅大幅提升Heliconical結構作為寬頻濾光元件之高度可控性與操作穩定性，亦為多波段反射、可動態調變與低功耗之元件提供實用化解決方法。;This study aims to address the inherent limitations of heliconical structures under high electric fields, specifically the narrowing of reflection bandwidth and the decline in reflectance caused by a decrease in birefringence (∆n) when reflecting shorter wavelengths, such as blue light. A novel two-stage photopolymerization method is proposed to enable low-voltage operation, high controllability, and broadband reflection in tunable optical filter devices. The experimental material system is based on a positive nematic liquid crystal (5CB), blended with liquid crystal dimers (CB7CB and CB11CB) and a chiral dopant (S811) to form the heliconical structures. A reactive mesogen (RM257) and photoinitiator (DMPAP) are introduced to enable ultraviolet (UV) photopolymerization. Initial investigations using a single-stage polymerization approach demonstrate that the heliconical structure undergoes a reduction in pitch and a change in cone angle upon UV exposure, resulting in a blue shift of the reflection peak and spectral broadening. However, this process is accompanied by a reduction in reflectance and unpredictable spectral shifts. To overcome these limitations, a two-stage polymerization method is developed. The first stage induces a non-uniform spatial distribution of pitch and cone angle, which broadens the reflection bandwidth, followed by the second stage where the structure is fixed under a designated target voltage. Experimental results show that this approach enables stable spectral broadening while maintaining high reflectance and significantly reducing the required driving voltage. Berreman matrix simulations confirm that the spectral broadening arises from the spatially non-uniform distribution of pitch and cone angle along the cell thickness. Moreover, the simulations provide insights into the structural evolution mechanism during the polymerization process. Overall, the proposed method significantly enhances the controllability and operational stability of heliconical structures as broadband reflective filters, offering a practical solution for multi-band reflection, dynamic tunability, and energy-efficient photonic devices.
