由於過渡金屬具有未屏蔽電子組態，故將其摻入晶體作為雷射增益介質可獲得極為寬頻之發光特性。在700-1000 nm波段，鈦藍寶石(Ti3+:sapphire)雷射已廣泛應用於寬頻可調雷射及鎖模雷射上。但在1200-1600 nm之光通訊波段，因摻Cr4+濃度低及熱效應問題，使得摻Cr4+雷射在此光通訊波段上進展受限。於本論文中，我們以共同提拉雷射加熱基座生長法生長出具雙纖衣(double-clad)結構之摻鉻釔鋁石榴石(Cr4+:YAG)晶體光纖(crystal fiber)，並將之以銀膠(silver gel)包覆作被動散熱(passive cooling)方式成功研製出室溫下斜率效率(18.1%)及最低激發閥值(62.6 mW)。當雷射運作溫度控制在13 oC下時，可獲得20.1%之高斜率效率及52.7 mW之低激發閥值。其中激發閥值相較文獻上塊材式之摻鉻釔鋁石榴石雷射低超過1個數量級以上。另一方面，本論文亦首次發現，因使用銀膠與銅鋁合金兩種不同封裝包覆造成Cr4+:YAG晶體光纖受到不同的封裝應力，分別在輸出特性上產生一段與兩段斜率效率也影響雷射輸出波長。雷射波長輸出與溫度相依性，代表此雙纖衣結構之Cr4+:YAG晶體光纖可提供較塊材(bulk)更大之增益。以上結果顯示，此雙纖衣晶體光纖雷射具有極高效率及極低激閥值。未來相當有潛力研製成通訊用之波長可調光纖雷射。此外，以具高空間解析率之近場掃瞄光學顯微鏡對Cr4+:YAG雙纖衣晶體光纖雷射之近場特性作分析，並與其遠場光學特性做一詳細之探討與比較。其近場光學實驗量測與模擬結果比對顯示，當多模(multimode)之Cr4+:YAG雙纖衣晶體光纖作為主動雷射元件時，可以極接近完美高斯之單模(single mode)作輸出，其光束品質因子(M2)約為1.1。此近場光學量測結果可為將來設計可調通訊用波長可調光纖雷射或鎖模(mode-locked)雷射提供一重要參考依據。最後我們也針對所研製之晶體光纖雷射進行模擬，其結果與實驗結果相符合。

Due to the nature of the unscreened electronic configuration, the transitional-metal-doped YAG can be used as the gain medium of lasers for broadband application. Ti3+: sapphire lasers have been widely used as tunable and mode-locked laser in the 700-1000 nm wavelength range. However the progress for the application of optical communication in the 1200-1600 nm wavelength range has been hindered by the problem of heat dissipation and low concentration of Cr4+ ion in tetrahedral position. In the thesis, we report continuous-wave Cr4+:YAG fiber lasers with a double-clad crystal structure grown by the co-drawing laser-heated pedestal growth method. The lasers operated in the room temperature have a slope efficiency of 18.1% and a threshold of 62.6 mW. Under the temperature of 13℃, the lasers have a better performance with a slope efficiency of 20.1% and a threshold of 62.6 mW. The lasing threshold of the lasers is an order of magnitude lower than the previous reported Cr4+:YAG fiber lasers. In this work, two different alloys, Cu-Al and silver gel, are used separately in laser packaging. The lasers with Cu-Al package show an output character of double-slope efficiency due to high strain built introduced by the package, while the lasers with silver gel package demonstrate ordinary output characteristics of single-slope efficiency. Temperature-dependent study shows that the Cr4+:YAG in the double-clad structure has much higher gain-bandwidth product than the crystal in bulk form. The high slope efficiency and low threshold characters of the Cr4+:YAG fiber laser with a double-clad structure have a potential use as tunable broadband lasers in the1200-1600 nm wavelength range. Further, the near-field and far-field characteristics of the lasers are obtained by a highly spatial resolved near-field scanning optical microscope. The experimental results agree well with the theoretical results. The output of this multimode Cr4+:YAG double-clad fiber lasers have nearly perfect Gaussian beam character with a beam quality factor M2 of about 1.1. The near-field characteristics offer a useful guideline for further fabricating broadband tunable lasers and mode-locked lasers in all-optical communication systems. Finally, some simulations of the laser output power have been developed to predict the experimental results.

致謝
中文摘要••••••••••••••••••••••••••••••••••••••••••••••••i
英文摘要•••••••••••••••••••••••••••••••••••••••••••••••ii
目錄••••••••••••••••••••••••••••••••••••••••••••••••••iv
圖目錄•••••••••••••••••••••••••••••••••••••••••••••••••vi
表目錄••••••••••••••••••••••••••••••••••••••••••••••••••x

第一章 緒論••••••••••••••••••••••••••••••••••••••••••••1
1.1 前言••••••••••••••••••••••••••••••••••••1
1.2 文獻回顧••••••••••••••••••••••••••••••••2
1.3 研究動機與目的•••••••••••••••••••••••••••5
1.4 論文架構••••••••••••••••••••••••••••••••5

第二章 Cr4+:YAG晶體••••••••••••••••••••••••••••••••••••7
2.1 Cr4+:YAG晶體之材料特性•••••••••••••••••••7
2.2 Cr4+:YAG晶體之光學特性••••••••••••••••••16
2.3 Cr4+離子電荷補償••••••••••••••••••••••••19

第三章 Cr4+:YAG雙纖衣晶體光纖••••••••••••••••••••••••••23
3.1 共同提拉雷射加熱生長法•••••••••••••••••••23
3.2 離子摻雜濃度分佈量測•••••••••••••••••••••31
3.3 折射率與螢光分佈量測•••••••••••••••••••••32
3.4 光纖傳輸模態••••••••••••••••••••••••••••37

第四章 Cr4+:YAG雙纖衣晶體光纖雷射 •••••••••••••••••••••••41
4.1 雷射元件之製備•••••••••••••••••••••••••••41
4.2 遠場雷射特性之量測架構••••••••••••••••••••53
4.3 遠場雷射特性之結果與分析••••••••••••••••••61
4.4 近場雷射特性之量測架構••••••••••••••••••••70
4.5 近場雷射特性之結果與分析••••••••••••••••••75

第五章 Cr4+:YAG雙纖衣晶體光纖雷射之最佳化 •••••••••••••••81
5.1 理論模擬架構•••••••••••••••••••••••••••••81
5.2 最佳化模擬分析•••••••••••••••••••••••••••88

第六章 結論與未來工作•••••••••••••••••••••••••••••••••••93
6.1 結論••••••••••••••••••••••••••••••••••••93
6.2 未來工作••••••••••••••••••••••••••••••••96

參考文獻••••••••••••••••••••••••••••••••••••••••••••••••97
中英對照表•••••••••••••••••••••••••••••••••••••••••••••104
附錄: Yb3+:YAG-silica單纖衣光纖雷射•••••••••••••••••••••108
簡歷••••••••••••••••••••••••••••••••••••••••••••••••••128

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