本研究主要探討了波導材料LiNbO3的L型和矩形偏振轉換器，利用其折射率的各向異性來轉換波導內入射光的偏振方向。我們使用有限時域差分法來模擬偏振光在波導中的傳輸的強度與偏振的變化。分析了不同尺寸的L 型波導和矩形波導結構，經過優化後，使偏振轉換效率可達到接近100%。針對 L 型偏振轉換器波導進行設計與分析，為了避免傳統蝕刻結構所帶來的製程困難，亦提出矩形波導作為替代方案。為加速兩種結構之尺寸優化流程，我們引入雙波導耦合理論，並推導出可預估偏振轉換的解析公式，以有效提升設計效率。並且在波導中施加電場改變折射率後，對偏振光轉換的影響。計算了調整輸出光偏振方向時所需的電壓強度，藉由此分析，評估電控偏振調制在LiNbO3偏振轉換器波導中的可行性與應用潛力。;This study investigates both L-shaped and rectangular polarization converters based on LiNbO₃ waveguide material, leveraging its refractive index anisotropy to achieve polarization conversion of incident light within the waveguide. The Finite-Difference Time-Domain (FDTD) method was employed to simulate the transmission and polarization conversion behavior of light propagating through the waveguide. Various geometrical configurations of both L-shaped and rectangular structures were analyzed, and after optimization, a polarization conversion efficiency approaching 100% was achieved. To overcome fabrication challenges associated with conventional etched structures, a rectangular waveguide design was proposed as an alternative. Coupled-mode theory was introduced to accelerate the dimensional optimization process, and an analytical formula was derived to estimate the polarization conversion efficiency, thereby improving design efficiency. Furthermore, the effect of applying an external electric field to alter the refractive index distribution within the waveguide was investigated, along with the resulting change in polarization conversion performance. The required voltage to achieve the desired output polarization state was also calculated. Based on these analyses, the feasibility and application potential of electrically controlled polarization conversion in LiNbO₃-based polarization rotator waveguides were comprehensively evaluated.
