並聯非線性光子晶體之光學軌道角動量光源研究

Abstract

本論文分成四個部分介紹:第一部分主要介紹相位匹配的概念；第二部分為干涉儀的架設與渦旋光的理論，在干涉儀的章節中會探討同調長度的影響與測量相位的方法，而在渦旋光的部分中將介紹其能量流方向與相位結構、渦旋光的生成方法並延伸到其特殊的干涉圖紋；第三部分為週期性極化鉭酸鋰晶體製程與結構設計，本研究中將會製作三種不同結構的晶體，探討其雷射本徵模態的變化；第四部份是利用並聯週期結構的非線性光子晶體生成HG模態與LG模態，並以干涉儀觀察其干涉圖紋。 在實驗中成功以並聯週期結構生成HG10與類HG20，並利用干涉的方法確認其相位的真實性。在渦旋光的生成中，利用一對柱狀鏡像散特性的π/2模態轉換特徵，產生出LG01，與不完美的LG02。同時也用干涉法，觀察到其LG模與平面波或球面波的叉狀與螺旋干涉圖紋。因此可以確定極化反轉所產生的折射率變化，會使得週期結構產生類似波導的現象，致使雷射模態與相位發生改變。

This thesis is divided into four main sections. The first section introduces the fundamental concepts of phase matching. The second section discusses the construction of the interferometer and the theory of vortex beams. In this part, the influence of coherence length and the methods for phase measurement are examined, while the vortex-beam subsection introduces the energy-flow direction, phase structure, various generation methods, and their characteristic interference patterns. The third section presents the fabrication and structural design of periodically poled lithium tantalate (PPLT) crystals. In this work, three different nonlinear photonic crystal structures are fabricated to investigate the resulting variations in laser modes. The fourth section focuses on generating the HG and LG modes using nonlinear photonic crystals configured in a parallel periodic structure, and the corresponding interference patterns are analyzed using an interferometer. In the experiments, HG₁₀ and HG₂₀-like modes were successfully generated using a parallel periodic structure, and their phase authenticity was verified through interferometric measurements. For vortex-beam generation, a π/2 mode converter based on the astigmatic properties of a pair of cylindrical lenses was employed to produce LG₀₁ and an imperfect LG₀₂ mode. Interference measurements also revealed the characteristic forked and spiral fringe patterns. These results confirm that the refractive-index variations induced by periodic poling can create a waveguide-like effect within the structure, which leads to changes in both the laser modes and their phase distributions.