LHPG 生長法晶纖微結構及成份分析

由前所述的試片製備方法，我們成功地在雙層纖衣結構之纖心部份以

獲得纖心與內層纖衣之高解析影像。雖然離子束減薄後的薄區面積並不是 非常的大，但已能夠讓我們成功地觀察到纖心與內層、外層纖衣界面之微 結構情形。

4.3.2.1 單層及雙層纖衣 Cr

:YAG 晶纖成分分析結果

為了解由fused-silica 玻璃包覆之 Cr⁴⁺:YAG 晶體光纖的化學組成，我們 將其鑲埋於導電碳中或以錫鉛合金作包覆，並於晶纖端面分別依序以砂紙 號數 400、600、800、1200 作研磨，然後依序以鑽石顆粒大小為 3、1、1/4 μm 作拋光。我們藉由 EPMA 來量測單層纖衣和雙層纖衣的成份。首先，

我們對雙層纖衣的晶體光纖做線掃瞄，圖 4-34為 EPMA 所拍下的端面圖。

圖 4-34中的白線(a)為 EPMA 所做的線掃瞄。

圖4-34 雙層纖衣晶體光纖 SEM 端面圖 纖心直徑為 16 μm 內層纖衣直 徑為90 μm[10]

圖4-35 雙層纖衣晶體光纖成分濃度分佈圖[60]

圖4-35是由LHPG 所生長的雙層纖衣晶體光纖成分濃度分佈圖。從圖 中我們可以很明確的看見，外層纖衣的部分完全皆由 SiO2所構成的，而內 層纖衣的部分，則是由 YAG 結構混合 SiO2所形成，最後纖心則完全是YAG 結構。從圖 4-35 中，我們可以發現很有趣的一點，那就是在內層纖衣中，

Y2O3的成分濃度幾乎是沒有變化的，而 Al2O3 的濃度則是漸漸的降低。而 且，我們還可以觀察到，Y2O3及 Al3O3由纖心往外擴散，到內層纖衣和外 層纖衣的交界處便是擴散的終點。

圖4-36 單層纖衣晶體光纖 SEM 端面圖 纖心直徑為 100 μm 圖 4-36 是由 LHPG 所生長的單層纖衣晶體光纖，一樣經過上述之研

圖4-37 LHPG 所生長的單層纖衣晶體光纖成分濃度分佈圖[60]

從圖 4-37中，我們可以觀察到纖心的部分，完全是 YAG 和 SiO2相互混合。

因此，我們和 LHPG 所生長的雙層纖衣晶體光纖來比較濃度分佈，可以斷 定這是在生長單層纖衣晶體光纖時，使YAG 完全熔化生長，SiO2使擴散至 纖心。而在生長雙層纖衣的晶體光纖時，因中心 YAG 熔化的並不像生長單 層纖衣晶體光纖時那麼完全，所以中心還保留著純 YAG 的成分。同樣的，

從圖 4-37中我們的可以觀察出，在纖心的部分，Al2O3漸漸的往纖衣處漸少。

4.3.2.2 LHPG 單層及雙層纖衣晶纖微結構分析

圖 4-38為 LHPG 生長法所提拉的雙纖衣晶體光纖 HRTEM 影像。從圖 4-38中，首先可以觀察到在纖心(Core)的位置是相當完美的結晶結構，其擇 區繞射如圖 4-39 所示。而在內層纖衣(inner clad)的部份，在外圍可以看到 有出現許多不同結晶相的奈米尺寸(crystalline nanopartical)結晶結構，在纖 心和內層纖衣介面處，可以看見纖心的晶格產生扭曲，這是為了和內層纖 衣中非晶(amorphous)的結構相結合所造成的晶格調變。而經由分析，發現 在內層纖衣靠近纖心處，存在著密度很高的奈米結晶結構，經由 TEM-SAD 分析後証明其結晶結構為 γ-Al₂O₃。

圖 4-38 LHPG 生長法所生長雙纖衣晶體光纖[10]

圖4-39 晶體光纖纖心處之擇區繞射圖

圖4-40 雙層纖衣中內纖衣結晶結構生長過程[10]

而圖4-40為LHGP 生長法成長之雙層纖衣晶體光纖內層纖衣中奈米尺 寸結晶結構之型變過程。圖4-40 (a)為 SiO₂一接觸到YAG，其 YAG 結晶結 構開始變化。而圖4-40 (b)；(c)；(d)是說明隨著SiO₂和YAG 相互擴散，存 在於內層纖衣之奈米結晶顆粒逐漸形成，且其結晶結構漸漸的從距 YAG 3 μm 到 12μm，主要為其形變應力場釋放之故。從這項分析，正好對應了 由圖 4-35 雙層纖衣成分濃度分佈中所描述的，在內層纖衣中 Al₂O₃逐漸的 向外層纖衣處減少。因為結晶相的成份為 Al₂O₃，當結晶相逐漸被 SiO₂ 往 外排出時，結晶相數逐漸增加而且向外排出，所以在 EPMA 中所才會看見 在內層纖衣中，其 Al₂O₃的濃度隨靠近外層纖衣而減少。

圖 4-41 則是 LHPG 生長法所生長的單層纖衣晶體光纖的 HRTEM 影 像，從圖中可以觀察出在纖衣處存在許多奈米尺寸結晶(紅色箭頭所標示)，

依 TEM-SAD 之分析這些晶相和雙層纖衣晶體光纖中，出現在內層纖衣的 晶相是相同的成分和結構，而由TEM 結構觀察發現，隨著愈靠近纖心其奈 米結構顆粒將形成聚集現象之 Claster 結構。

圖4-41 單層纖衣高倍率放大影像[60]

更進一步觀察發現圖4-42中，在愈靠近纖心處甚至出現更明顯之結晶 相聚集而形成晶界，主要係結晶結構的數量越多，當許多小晶相的距離很 靠近的時候，小結晶相會彼此聚集，如此可能形成較大之微米尺寸結晶 (micropartical crystalline)。雖然在目前之 HRTEM data 中於纖心處並未觀察 到微米之 Cluster 結構，但由晶界之形成，證明此種結構可能存在於單纖衣 之晶纖中，未來將對此部份做更深入的研究。

圖4-42 LHPG 生長法單層纖衣晶體光纖中靠近纖心產生晶界之 HRTEM 影 像[10]

由第四章中得知雙層纖衣晶體光纖的ASE 值比單纖衣晶體光纖的 ASE 值要高。部分原因應為單層纖衣晶體光纖中可能存在的微米尺寸的結晶顆 粒較雙層纖衣晶體光纖多，故單層纖衣晶體光纖產生之米氏散射情況較雙 層纖衣晶體光纖為高。如圖 4-43為 LHPG 生長法單層纖衣晶體光纖顯微結 構示意圖。故有關於此種奈米結構和微米結構之形成是否影響光纖傳輸性

Grain boundary Grain boundary

Grain boundary

質，將是未來微結構研究之一大重點。

圖4-43 LHPG 生長法單層纖衣晶體光纖顯微結構示意圖

第五章---結論與未來研究規劃

1. 持續深入分析 LHPG 法晶體光纖不同拉製速度以及不同的 CO2 雷射 強度下之雙層纖衣界面結構及奈米結晶相之熱擴散及聚集現象，對 晶體光纖傳輸損耗特性之影響。

2. 改善抽絲塔法晶體光纖之拉製速度以及抽絲參數，再觀察其奈米結 晶相之變化，並進嘗試生長雙層纖衣晶體光纖結構，以期待較佳之 波導效果。

3. 藉由 IAD 輔助晶體光纖側鍍，來進一步提高其鍍膜緻密性，進而提 高其晶纖雷射增益。

4. 為之進一步分析 LHPG 以及抽絲塔生長法各種不同拉製參數製程下 之晶纖微結構觀察，不斷精進及改良 HRTEM 試片製作過程也將是 未來之主要研究工作之一。

5. 而藉由 CaO 側鍍結果發現確實能有效的提升 Cr⁴⁺的濃度，而提高其 晶纖雷射增益。另在微結構研究中亦發現，若在輔以O₂環境下退火 處理，將可有效降低其晶纖表面之缺陷結構，而提高其晶纖品質，

降低折射率以及螢光強度。

6. 嘗試藉由TiO₂側鍍來提升 Cr⁴⁺的濃度，來提高其晶纖折射率和螢光 強度。

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