由於近年來光通訊頻寬需求急速增加，使得研製具有超寬頻特性之增益介質成為一重要課題。其中，以摻鉻釔鋁石榴石(Cr4+:YAG)於光通訊波段具有3 dB頻寬高達265 nm之超寬頻特性最受矚目。本實驗室已成功以共同提拉雷射加熱基座生長法(co-drawing laser-heated pedestal growth method)研製出具有波導結構、低損耗及低激發閥值(low threshold)之Cr4+:YAG雙纖衣晶體光纖(Cr4+:YAG double-clad crystal fiber; Cr4+:YAG DCF)超寬頻光源、光放大器及雷射，顯示Cr4+:YAG雙纖衣晶體光纖在未來光通訊中極具有潛力取代目前之摻鉺光纖(erbium doped fiber)。
為了進一步提升上述Cr4+:YAG DCF所研製之主動元件的效率，本論文以近場掃描光學顯微鏡(near-field scanning optical microscope; NSOM)，量測位於Cr4+:YAG DCF纖心(core)之近場光譜特性，分析因纖心與內層纖衣(inner cladding)之熱膨脹係數不同所產生之應力(strain)變化分佈、螢光生命週期(fluorescence lifetime)及纖心尺寸三者之相互關係。結果顯示纖心直徑20 μm時，存在纖心所受應力趨近於0；且纖心直徑20 μm比11 μm之Cr4+螢光生命週期及幅射截面積各增加6.34%及19.17%。
此外，本論文亦首次藉由NSOM研究Cr4+:YAG DCF放大自發輻射(amplified spontaneous emission; ASE)及雷射之近場光學特性及輸出模態。結果證明當元件產生雷射輸出時，其光束品質參數M2 ~1.1，顯示Cr4+:YAG DCF雷射為一接近理想高斯光束之單模(LP01)光源，可進一步作為後續研製可調波長雷射(tunable laser)之基礎; 於ASE方面顯示，當模態數為4時，單模所佔比例約為26%；當模態數為7時，單模所佔比例快速下降至約15%，此近場模態量測結果亦可為未來將寬頻ASE光源耦合進單模光纖，提供重要參考依據。
μμ

With the escalating demands for optical communication network system, the need for broadband gain medium in optical communication has increased. Among them, Cr4+:YAG crystal has shown an exceptionally successful broadband amplified spontaneous emission (ASE) light source that fully cover 1.2-1.6 μm range (3-dB bandwidth up to 265 nm). More recently, we demonstrated the realization of a waveguiding, low-loss, and low-threshold Cr4+:YAG double-clad crystal fiber (DCF) based ultra-broadband ASE light source, optical amplifier, and laser grown by the co-drawing laser-heated pedestal growth technique. These results demonstrate the potential of the Cr4+:YAG DCF for the replacement of the erbium doped fiber in future optical communications.

To further improve the efficiency of Cr4+:YAG DCF based active devices, here we show the difference in thermal expansion coefficients between a YAG core and an inner cladding creates a significant localized strain field by near-field scanning optical microscope (NSOM), which can result in optical confinement and provide the possibility to simultaneously alter the Cr3+ and Cr4+ fluorescence lifetime with varied core dimensions. The results indicate that There exists a nearly zero strain across the entire core with a diameter of ~20 μm, which is beneficial the higher Cr4+ fluorescence lifetime (+6.43%) and emission cross section (+19.17%) as compared with 11-μm core.

In addition, we have successfully investigated the near-field modal characteristics of Cr4+:YAG DCF laser and ASE by NSOM. The results demonstrate that the Cr4+:YAG DCF laser produced nearly a single-mode (LP01) output with diffraction-limited beam quality of M2 ~1.1; for ASE, the modal weighting of LP01 decreases from 26% to 15% as the number of modes increases from 4 to 7. The results offer a guideline not only for further fabricating Cr4+:YAG DCF tunable lasers, but for efficiently coupling a broadband ASE light source into a single-mode fiber.

中文摘要i
英文摘要ii
致謝iii
目錄iv
圖目錄vi
表目錄xi
第一章 緒論.1
第二章 近場掃描式光學顯微鏡之原理與架構3
2.1近場之定義3
2.2近場掃瞄式光學顯微鏡架構6
2.3近場光侷限機制7
2.4近場距離維持機制10
第三章 Cr:YAG晶體之特性14
3.1 Cr:YAG晶體14
3.2 Cr3+:YAG能階、吸收及放射光譜20
3.3 Cr4+:YAG能階、吸收及放射光譜24
3.4應力對於Cr3+及Cr4+螢光光譜之影響27
第四章 Cr:YAG雙纖衣晶體光纖之生長與檢測32
4.1雷射加熱共同提拉生長法32
4.2 Cr:YAG雙纖衣晶體光纖之成分分析39
4.3 Cr:YAG雙纖衣晶體光纖之傳輸特性.42
第五章 Cr:YAG雙纖衣晶體光纖之應力量測與分析52
5.1 Cr:YAG雙纖衣晶體光纖試片之製備52
5.2近場光學量測架構56
5.3具纖心內應力之螢光光譜特性59
5.3.1 Cr3+近場光學量測與分析59
5.3.2 Cr4+近場光學量測與分析64
5.3.3 Cr:YAG雙纖衣晶體光纖之Cr3+和Cr4+螢光比
較分析70
第六章 Cr4+:YAG雙纖衣晶體光纖主動元件之近場光學量
測與分析72
6.1 Cr4+:YAG雙纖衣晶體光纖雷射元件之製備72
6.2 Cr4+:YAG雙纖衣晶體光纖雷射之近場量測
架構76
6.3 Cr4+:YAG雙纖衣晶體光纖雷射之近場特性77
6.4 Cr4+:YAG雙纖衣晶體光纖放大自發輻射之
近場特性81
第七章 結論與未來工作85
參考文獻87
中英對照表92

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