摻鉻光纖具有自發輻射特性，其頻段可涵蓋整個低損耗商用玻璃光纖通訊波段1.3-1.6 m，因此摻鉻光纖具有潛力發展成寬頻光纖放大器，增加光纖通訊系統傳輸容量及可調應用性。特殊摻鉻光纖纖心材質以晶體為主，惟最大挑戰方向為如何製作出單模態傳輸摻鉻晶體光纖，單模態傳輸於具增益特性的晶體光纖中，能展現創新技術於放大器應用。
近年本實驗室研究製作摻鉻晶體光纖的方法有以下兩種:(1) 利用改良式雷射基座加熱生長法(Laser-heated pedestal growth, LHPG)製作少數模態雙層纖衣摻鉻晶體光纖，其方法為多次重複加熱擴散機制縮小纖心直徑。(2) 利用雷射基座加熱生長法(LHPG) 生長摻鉻晶體光纖及抽絲塔拉製與Cr:YAG 折射率接近之高折射率玻璃(N-SF57)管，再用高折射率玻璃管包覆摻鉻晶體光纖，製作成少數模態與單模態高折射率玻璃包覆摻鉻晶體光纖。
本論文已研製三種摻鉻晶體光纖；少數模態雙層纖衣摻鉻晶體光纖，少數模態高折射率玻璃包覆摻鉻晶體光纖及單模態高折射率玻璃包覆摻鉻晶體光纖，兹將量測遠場模態與增益特性說明如下。(1) 纖心直徑2 m與長度2 cm之少數模態雙層纖衣摻鉻晶體光纖，其在訊號光1400 nm於遠場模態量測上能展現LP11 之少數模態特性。而增益量測於雙端激發的架構下，訊號光波長1400 nm、激發光波長1064 nm與激發光總功率200 mW，可得到光增益(Gross gain) 2.3dB(1dB/cm)，但研製較長長度少數模態雙層纖衣摻鉻晶體光纖具困難度且整體製程良率不佳。(2) 少數模態高折射率玻璃包覆34m長度9.8 cm之摻鉻晶體光纖，其在訊號光1400 nm遠場量測上亦呈現LP11，此少數模態高折射率玻璃包覆摻鉻晶體光纖在提升製程良率與增益特性上較少數模態雙層纖衣摻鉻晶體光纖佳。目前利用高折射率玻璃包覆晶體之少數模態摻鉻晶體光纖方法可產生較佳之光增益，於雙端激發光1064 nm波長在總功率400 mW與訊號光波長1400 nm時為4.1 dB (0.45dB/cm)。(3) 高折射率玻璃包覆直徑25m長度6.7cm之單模態摻鉻晶體光纖，在訊號光1400nm遠場量測到單模態特性LP01。單模態高折射率玻璃包覆晶體光纖在整體量測中可降低系統損耗而有淨增益(Net gain)特性，單端激發便可產生光增益為2.7dB (loss 0.4dB/cm)淨增益為 0.7 dB，故單模態摻鉻晶體光纖最具有潛力應用於光纖通訊之光放大器。
本論文已研製高折射率玻璃之單模態摻鉻晶體光纖及其光增益與淨增益量測，惟研究成果有待提升，期望進一步研發達成單模態寬頻譜光纖放大器應用於光纖通訊系統上。未來研發可嘗試利用其他材質之高折射率玻璃，例如: LaSF30的熱膨脹係數(7.1×10-6)比起N-SF57(9.9×10-6)小，使包覆晶纖過程能減少缺陷，期望單模態晶體光纖訊號光傳輸損耗降至0.02 dB/cm。並且研製長度較長(15cm 以上)，直徑小於25m單模態摻鉻晶體光纖，以用於提升光增益及獲得更高淨增益光纖放大器應用於光纖通訊系統。

Chromium-doped fiber (CDF) exhibits spontaneous emission characteristic which can cover the entire low-loss optical fiber communications band 1.3-1.6 m. Therefore, the CDF has the potential to increase transmission capacity and flexible applicability to develop the broadband optical amplifiers in optical fiber communication systems. The core material of the CDFs is a crystal-based and the challenge issue is to make the single-mode transmission in chromium-doped crystal fiber. Single mode transmission of the CDF exhibits gain characteristic crystal fibers and may demonstrate its innovative technology for amplifier application.
In this study, there were two methods for the chromium-doped crystal fiber fabrication. (1) The modified laser heated pedestal growth method (Laser-heated pedestal growth, LHPG) was used to fabricate the few mode Cr-doped double cladded crystal fibers. This method was the repeated heating diffusion mechanism to narrow core diameter. (2) The Cr:YAG crystal fibers and the high-index glass tube (N-SF57) were fabricated by LHPG method and drawing tower technology, respectively. Then, the Cr:YAG crystal fiber was inserted into high-index glass tube. Finally, the few-mode and single-mode Cr:YAG crystal fibers were obtained.
In this dissertation, three different kinds of chromium-doped crystal fiber have been fabricated: few mode chromium doped fiber cladded double crystal fiber (FMCDCCF), few mode chromium doped fiber cladded (FMCDCCF) by high refractive index glass, and single-mode chromium doped fiber cladded (SMCDCCF) by high refractive index glass. The far-field mode and gain characteristics of the CDFs are measured and demonstrated as below. (1) The FMCDCCF showed the LP11 mode by far-field pattern measurement. A FMCDCCF of 2 µm in core diameter and 20 mm in fiber length with gross gain of 2.3 dB (1dB/cm) was demonstrated by pumping power of 200 mW. However, the growth process was complex and difficult to repeat. (2) The FMCDCCF of core diameter 34 m and fiber length 9.8cm was cladded by high-index glass (N-SF57). The far-field pattern of LP11 mode could guide by FMCDCCF cladded by high-index glass. Through utilized double-pumping method, a 4.1-dB (0.45dB/cm) gross gain at the signal wavelength of 1.4μm was obtained by the pumping power of 400mW. So, the gain performance of high-index glass cladded FMCDCCF was better than the FMCDCCF. (3) The SMCDCCF by cladded high-index glass of 25 m and 6.7cm in fiber length was demonstrated LP01 mode by far-field pattern measurement. The SMCDCCF exhibited a gross gain of 2.7 dB (0.4dB/cm) and a net gain of 0.7 dB at the wavelength of 1.4 μm was demonstrated by single pumping power of 320 mW. Overall, the SMCDCCF exhibited lower pumping power loss than the FMCDCCF.
This study provided a novel method for fabricating single-mode Cr-doped crystal fibers (SMCDCCFs). The SMCDCCFs exhibited gross gain and net gain of Cr-doped crystal fibers. However, higher gross gain and net gain should be improved. Further development of 10 dB net gain of the SMCDCCFs is important to reach a broadband spectrum of fiber amplifiers in optical fiber communication systems. In the future, our research may try to use other materials of high refractive index glass. For example, SMCDCCFs also can clad by the LaSF30 (7.1×10-6) which has the lower thermal expansion coefficient difference than N-SF57 (9.9×10-6). The defects of SMCDCCFs may be reduced during growth process. We expect that the optical loss of SMCDCCFs clad by new high-index glass may reduce to 0.02 dB/cm. The development of the longer length (above 15 cm) and smaller core diameter( below 25 m) of the SMCDCCFs for higher gross gain and net gain is necessary and important. Therefore, the SMCDCCF has the potential to be used as the fiber amplifiers in optical communications.

論文審定書…………………………………………………………… i
誌謝…………………………………………………………………. iii
中文摘要………………………………………………………….…..iv
英文摘要………………………………………..…………………….vi
第 一 章 緒論…………………………………………………........ 1
1.1研究動機………..……………………………………………....1
1.2文獻探討…..…………………………………………………....1
1.3章節簡述……..…………..………………..………………….. 5
1.4參考文獻………..…………………………………………….. 6
第 二 章 晶體光纖與少數模態晶體光纖之製程..…………........ 7
2.1利用雷射加熱基座生長法(laser heated pedestal growth, LHPG)
生長晶體光纖……..…………………………………………....7
2.2雙層纖衣晶體光纖生長………..……………………………. 16
2.3高折射率包覆晶體光纖生長………..………………………. 21
2.4參考文獻………..……………………………………………. 28
第 三 章 Cr4+:YAG材料與光學特性.…………………..…....... 30
3.1釔鋁石榴石結構材料簡介………..…………………………. 30
3.2摻鉻晶體之光學特性………………..………………………. 40
3.3雙層纖衣晶體光纖元素組成檢測………..…………………. 43
3.4雙層纖衣內纖心晶體結構分析………..……………………. 49
3.5雙層纖衣晶體光纖內纖心端面檢測….…….………………. 54
3.6參考文獻…………………………….……….………………. 57
第 四 章 晶體光纖元件量測特性與實驗結果…………………. 60
4.1光纖波導…………………….…..…………………………….60
4.2晶體光纖損耗……………….…..…………………………….64
4.3晶體光纖折射率量測………………...……………………….69
4.4晶體光纖螢光量測………..…………………………………. 72
4.5晶體光纖模態量測………..…………………………………. 74
4.6增益特性量測………..………………………………………. 77
4.7參考文獻………..……………………………………………. 88
第 五 章 研究結論與未來方向………..……………………..... 91
5.1研究討論………..……………………………………………. 91
5.2參考文獻………..……………………………………………. 96

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