李世光臺灣大學：應用力學研究所陳志豪Chen, Chin-HaoChin-HaoChen2007-11-292018-06-292007-11-292018-06-292007http://ntur.lib.ntu.edu.tw//handle/246246/62424奈米光學、光子晶體與表面電漿為近年蓬勃發展的光學研究，次波長結構與近場下的光學現象在奈米科技熱潮引領的研究上也發現越來越多的應用。在如此微小尺度下的光學現象，傳統光學遠場成像已面臨瓶頸，近場光學顯微鏡為具有突破繞射極限限制的光學儀器，以近場的方式擷取高解析度的影像，由於相關技術的突破與相關光學現象的深入了解，使得近場光學顯微鏡成為探索奈米光子學的必要工具。 一般光電偵測都是量測光強訊號，無法完整分析光場的特性，而相位偵測有較光強更好的敏感性，本論文以干涉方式取相完成近場光學顯微鏡量測相位的能力，將原本近場光學系統結合外差光纖干涉儀之實驗架構，具有高精度與高感度的優點，對於高頻近場光學訊號的指數衰減特性以及光纖探針位提升解析度縮小孔徑造成導光能力大幅下降，在外差干涉偵測下提高訊號的對比，降低放大弱光訊號所造成的雜訊，提升了近場光學顯微鏡的性能。除訊號提昇之外，亦可分析近場下的相位資訊，從相位資訊中可以了解電磁波的傳遞以及光場的特性。 本系統涵蓋近場光學顯微鏡系統、光纖干涉感測、外差移頻技術、光電偵測信號處理與抗雜訊與環境干擾方法，完成建構近場外差干涉儀，並以聚焦光點、繞射光柵與次波長表面結構驗證整體系統在量測訊號上提升的能力，證實相位資訊更能敏感反應電磁場傳遞變化。Nanophotonics, photonic crystal and surface plasmons are hot topics in optics research in recently years. Optical phenomena in subwavelength structure and near- field region had been applied to many applications in this nano-technology trend. Conventional optical microscopy had encountered bottleneck in such small scale because of the far-field image resolution. Near-field scanning optical microscopy (NSOM) is the instrument which can overcome the diffraction limit by getting high resolution image in near-field region. By the development of related techniques and the knowledge of near-field optics, NSOM becomes the essential measurement tool for nanophotonics. Photodetection generally transfer light intensity to electric signal, so it cannot analyze the complete characteristics of light field. Phase detection is more sensitive than intensity detection. In this thesis, interferometry is added into NSOM to measure the optical phase. The combination of NSOM system and heterodyne fiber interferometer has shown high precision and high sensitivity ability. Because of the exponential decay of high spatial frequency near-field optics and much smaller aperture of high resolution fiber tip, the optical signal is very weak. Heterodyne interferometer can enhance the contrast of signal and decrease the noise of amplifying low level signal. Besides improving the NSOM signal, heterodyne interferometer can help to get phase information which leads to better understanding of the electromagnetic wave propagation characteristics of light field. This system contain near-field scanning optical microscopy, fiber interferometer, heterodyne technique, photodetecion, signal processing, noise reduction and environment control method. Experiments of focus spot, diffraction grating and subwavelength surface structure confirm the low-level signal measurement ability of the near-field heterodyne interferometer and further verify the higher sensitivity achieved by using the phase detection to examine the electromagnetic wave propagation behaviors.誌謝 I 中文摘要 III Abstract V 目錄 VII 圖表目錄 X Chapter 1 序論 1 1.1. 顯微鏡與繞射極限 1 1.2. 近場光學顯微鏡 2 1.3. 文獻回顧與研究動機 4 1.4. 論文架構 5 Chapter 2 理論 7 2.1. 遠場光學 7 2.1.1 繞射公式 8 2.1.2 圓環孔洞的繞射 9 2.2. 高斯光束 10 2.3. 聚焦電磁理論 12 2.4. 近場光學 15 2.4.1 光纖探針 17 2.4.2 表面電漿 19 2.4.3 電磁模擬 22 2.5. 外差式干涉儀 23 2.6. 外差式干涉訊雜比 25 Chapter 3 實驗架構 28 3.1. 光纖干涉儀 28 3.1.1 光纖干涉儀偏極態 29 3.1.2 光纖接合 30 3.1.3 光纖干涉儀相位穩定度 32 3.2. 鎖相放大器 33 3.3. 調變機制 36 3.4. 聲光調變器 39 3.5. 差頻電路 41 3.6. 近場光學顯微鏡 45 3.6.1 光源 48 3.6.2 光電倍增管 50 3.6.3 光電二極體 51 3.6.4 光纖的光電偵測 53 3.7. 近場干涉儀 54 3.7.1 實驗細部調整 58 3.7.2 系統雜訊 59 3.7.3 環境控制 61 Chapter 4 實驗結果 63 4.1. 光纖外差干涉儀系統分析 63 4.1.1 強度衰減特性 63 4.1.2 偏極態試驗 64 4.1.3 環境影響 65 4.2. 量測驗證 66 4.2.1 焦點 66 4.2.2 光柵 69 4.3. 次波長圓環 73 4.3.1 試片製作 73 4.3.2 遠場繞射場型 73 4.3.3 近場圖形 75 Chapter 5 結論與未來展望 78 5.1. 結論 78 5.2. 未來展望 79 5.2.1 系統優化 80 5.2.2 量測應用 81 Reference 83en-US近場光學顯微鏡光纖干涉儀外差干涉近場光學near-field optical microscopyfiber interferometerheterodyne interferometernear-field opticsthesis