2006-08-012024-05-14https://scholars.lib.ntu.edu.tw/handle/123456789/658768摘要：對摻鉻光纖而言，鉻離子的氧化態及YAG纖心與silica纖衣之界面特性，是影響信號增益及傳輸損耗的兩大因素。比起摻鉻之silica纖心而言，鉻離子在YAG中可大幅提昇四價鉻之比率，因而可有較高之增益，但相較於silica纖心之摻鉻光纖而言，由於YAG之折射率 (n=1.82)比起silica (n=1.45)大了不少，因此界面品質對傳輸損耗將有很大之影響。此外，經由快速的光纖抽絲塔所抽出的YAG纖心之摻鉻光纖，亦需經由氧環境退火以提升四價鉻比率及改善YAG/silica界面。目前以雷射加熱基座生長法已產生毫瓦級的超寬頻ASE光源，最新之成果將刊登於Optics Letters, March 2004，我們將延續此一成果，對YAG纖心與silica纖衣之摻鉻光纖研發以降低傳輸損耗並提昇增益。 本分項計畫擬以共焦顯微術及解析式電子顯微術在不同抽絲環境及退火條件下，研究摻鉻纖心之增益分佈、纖心/纖衣之折射率分佈及界面缺陷，此外由於鉻離子之增益頻譜對環境敏感，因此我們亦將研究不同抽絲環境及退火條件下，鉻離子之增益頻譜變化，並加以理論分析，計算激發輻射截面積(stimulated emis<br> Abstract: Two major factors that affect the signal gain and propagation loss in Cr doped YAG-core fiber are the oxidation state of Cr ion and the interface property between YAG core and silica cladding. Comparing to the Cr doped silica core, the ratio of Cr4+/Cr3+ is much higher in YAG; therefore, the gain of Cr:YAG is much higher than Cr:silica. However, the index of YAG (n=1.82) is larger than that of silica (n=1.45), the propagation loss of YAG core may be larger than silica core if the core/cladding interface is not properly treated. Using fiber drawing tower to pull the YAG-core fiber may result in residual stress in the core region, and should be annealed in oxygen environment to improve the core quality and raise the Cr4+ content. Our latest result on LHPG grown glass-clad Cr:YAG will be published in Optics Letters, March, 2004. We will continue the research along this line, and develop YAG-core and silica-clad Cr fiber to reduce the propagation loss and increase signal gain. In this sub-project, we propose to study the gain distribution in the core, and the index and defect profiles across the core/cladding using confocal microscopy and analytical electron microscopy. Since the Cr ion fluorescence is sensitive to its local crystal environment, it will be studied at various fiber drawing and annealing conditions. Theoretical analysis on the gain bandwidth product and experimental verification will be conducted to compare with that of by the laser heated pedestal growth method. The fluorescent lifetime is also an important factor for the optical conversion efficiency, especially when the Cr4+ concentration is beyond 2x1017 cm-3. We will measure the fluorescent lifetime as well as the cross section of excited state absorption, and adopt them in the rate equations to evaluate the conversion efficiency and utilize them to optimize the fabrication processes. In the first year, we will measure the propagation loss and amplified spontaneous emission of the Cr doped fiber. Multi-wavelength confocal microscope will be employed to acquire the index profile and the distribution of Cr4+/Cr3+ ratio. In the second year, we will anneal the drawn fiber at oxygen environment to raise the Cr4+ concentration. A time resolved confocal fluorescence microscope will be established to obtain the fluorescent lifetime and emission cross section. In the third year, we will make an attempt to use both CaO and MgO as charge compensators so that the quality of the YAG core can be improved and the charge compensation efficiency can be raised. The interface quality at the YAG/silica boundary will be improved using thermal annealing to reduce the propagation loss below 0.1 dB/m.光通訊光纖光放大器optical communicationoptical fiberfiber amplifier