將塊材晶體拉成晶體光纖適合用於光通訊領域之雷射、自發輻射放大光源、光放大器等元件，因其幾何結構與玻璃光纖類似，再者光纖結構可將泵激光源侷限在一個小的截面積上行進一長距離，而能維持高的能量密度。在晶體光纖生長技術方面，本研究採用雷射加熱基座生長法，此法無坩鍋污染問題，因此可生長出純度高及缺陷低的單晶，然而，晶體光纖的界面損耗是造成光損耗的主要因素之一，為了降低此光損耗以得到高的元件性能，適當的晶體光纖包覆是重要的。

在雷射應用上，我們使用具漸進式折射率分佈之晶體光纖研製出高效能的摻釹釔鋁石榴石(Nd:YAG)雷射，其研究方法是藉由控制主動離子之分佈，造成晶體光纖內部中心點和邊緣折射率差達到0.0284，使得雷射光被侷限在晶體光纖的中心區域，而降低界面損耗。目前已可得到80 mW的雷射輸出，其斜率效率為28.9%，此斜率效率為目前世界上以半導體雷射作為泵激光源所製成之Nd:YAG晶體光纖雷射之斜率效率最高者。

在自發輻射放大光源和光放大器應用上，由於摻鉻釔鋁石榴石(Cr4+:YAG)其自發輻射頻譜剛好涵蓋了整個低損耗窗口之光纖通訊波段，因此選用Cr4+:YAG 晶體光纖做研究。為了縮小晶體光纖直徑和降低傳輸損耗，我們開發出一新的包覆晶體光纖技術，稱為共同提拉雷射加熱基座生長法，雖然以fused silica包覆之晶體光纖其纖心直徑為29 micron且其傳輸損耗小於 0.1 dB/cm，此值較無包覆的晶體光纖小了7倍，但因為纖心含二氧化矽，造成了幾乎沒有Cr4+螢光。藉由控制適當的共同提拉雷射加熱基座生長法之生長參數，我們成功地生長出纖心直徑為25 micron之雙纖衣晶體光纖，其產生的自發輻射放大光源之功率及頻寬可達2.36 mW和265 nm。在將雙纖衣晶體光纖和傳統單模光纖做熔燒接合後，我們成功研製出世界上第一個適用在光纖通訊波段之摻雜過渡金屬的光纖放大器，其最高增益在輸入訊號光波長為1.47 micron下，可達16 dB。

Pulling bulk crystal into fiber is suitable for laser, amplified spontaneous emission (ASE), and optical amplifier applications in optical communications because of its structural similarity to silica fiber. Moreover, fiber configuration can confine pump light in a small cross-sectional area with a high energy density for a long distance. Among crystal fiber growth techniques, the laser-heated pedestal growth method (LHPG) was adopted. It is crucible free and can therefore produce high-purity, low-defect-density single crystals. However, interface loss of the crystal fiber is one of the main causes of optical loss. In order to reduce the optical loss, a proper method to clad the fiber is important for high device performance.

For laser application, high-efficient Nd:YAG lasers were demonstrated using gradient-index crystal fibers. We used controlled profile of the active ion resulted in index difference of 0.0284 between the center and the edge of the fiber to confine the laser beam in the center region and thus reduced the interface loss. A laser output power of 80 mW was achieved with a slope efficiency of 28.9%, which, to our knowledge, is the highest ever achieved for diode-laser-pumped Nd:YAG fiber laser.

For ASE and optical amplifier applications, Cr4+:YAG crystal fiber was studied due to its fluorescent spectrum just covering the low loss window of silica optical fiber. To reduce the fiber diameter and propagation loss, a novel cladding technique, codrawing LHPG (CDLHPG), was developed. Although fused-silica-clad fiber can be made with a 29-micron-diameter core and a propagation loss of less than 0.1 dB/cm, which is a factor of 7 smaller than that of an unclad fiber, it has almost no Cr4+ fluorescence in the core area due to the entering of SiO2 in YAG. With proper controlled growth parameters of the CDLHPG method, a double-clad fiber with a core diameter of 25 micron was successfully grown. Up to 2.36 mW of ASE with a bandwidth of 265 nm was demonstrated. After splicing the double-clad fiber with conventional single mode fiber, we successfully demonstrated the first transition metal-doped fiber amplifier in the optical fiber communication band. Up to 16-dB of gross gain at 1.47 micron was achieved.

中文摘要………………………………………………………………………… i
Abstract ………………………………………………………………………… ii
Table of Contents …………………………………………………………….… iii
List of Tables…………………………………….……………………………… v
List of Figures……………………………………………………………...…… vi

Chapter 1 Introduction ………………...……………………………………… 1

Chapter 2 Laser-heated pedestal growth system …..………………………… 6
2.1 Single crystal fiber growth ………………………………………... 6
2.2 LHPG apparatus …………………………………………………... 9
2.3 Fabrication process of single-crystal fiber ………………………... 11

Chapter 3 Nd3+:YAG crystal fibers ……...……………………………………. 15
3.1 Properties of Nd3+:YAG crystal …………………………………… 15
3.2 Characterization of Nd:YAG crystal fiber 18
3.2.1 X-ray diffraction analysis …………………………………..…. 18
3.2.2 Composition analysis ……………………………………..…... 19
3.2.3 Refraction index measurement ………………………………… 21
3.3 Nd:YAG crystal fiber laser ………………………………………... 25
3.3.1 Fabrication of Nd:YAG fiber laser ………………………...…... 25
3.3.2 Characterization of Nd:YAG fiber laser ………………….…….. 28

Chapter 4 Simulation of Cr4+:YAG crystal fiber devices …………………… 32
4.1 Properties of Cr4+:YAG crystal ……………………………………. 32
4.2 Rate equation analysis …………………………………………….. 37
4.3 Simulation of ASE light source …………………………………… 39
4.4 Simulation of laser ………………………………………………... 41

Chapter 5 Characterization of Cr4+:YAG crystal fibers …………………….. 49
5.1 Single crystal fiber ………………………………………………... 49
5.1.1 X-ray diffraction analysis ……..………………………………. 49
5.1.2 Composition analysis ………………………………………..... 50
5.1.3 Oxidation state analysis ……………………………………...... 53
5.2 Single-clad crystal fiber …………………………………………... 59
5.2.1 Growth of single-clad crystal fiber …………………………….. 59
5.2.2 Composition analysis ………………………………………..... 61
5.2.2.1 Electron probe microanalysis …………………………………... 61
5.2.2.2 Cr ion fluorescence measurements …..………………………….. 62
5.3 Double-clad crystal fiber ………………………………………….. 63
5.3.1 Growth of double-clad crystal fiber ……………………………. 63
5.3.2 Composition analysis ………..………………………………... 64
5.3.2.1 Electron probe microanalysis ………….……………………….. 64
5.3.2.2 Cr ion fluorescence and refraction index measurements ………..….. 65
5.3.3 Microstructure analysis using high-resolution TEM ……….…… 67
5.3.3.1 Microstructure of core ………………………………………… 67
5.3.3.2 Microstructure of inner cladding ……………..………………… 70
5.3.3.3 Comparison between inner cladding and outer cladding …...………. 73
5.3.3.4 Comparison of inner cladding with different growth speeds ………... 74
5.4 Propagation loss measurement ……………………………………. 77

Chapter 6 Applications of Cr4+:YAG crystal fibers ………………….……… 80
6.1 ASE light source …………………………………………………... 80
6.1.1 Single crystal fiber ………………………………………...….. 80
6.1.2 Single-clad crystal fiber …………..…………………………… 82
6.1.3 Double-clad crystal fiber …………………………………..….. 84
6.2 Double-clad crystal fiber amplifier ……………………………….. 88
6.2.1 Fusion of a double-clad fiber with a single-mode fiber …………. 88
6.2.2 Characterization of double-clad fiber amplifier ……...…………. 91

Chapter 7 Conclusions and future work ……………...……………………… 96
7.1 Conclusions ……………………………………………………….. 96
7.2 Future work ……………………………………………………….. 98

References ………………………………………………………………………. 100
Biography ……………………………………………………………………….. 109
Publication List………………………………………………………………….. 110

Chapter 1
[1.1] R. S. Feigelson, “Pulling Optical Fibers,” Journal of Crystal Growth 79, 669 (1986).
[1.2] M. M. Fejer, J. L. Nightingale, G. A. Magel, and R. L. Byer, “Laser-heated Miniature Pedestal Growth Apparatus for Single-crystal Optical Fibers,” Review of Scientific Instruments 55, 1791 (1984).
[1.3] M. J. F. Digonnet, C. J. Gaeta, and H. J. Shaw, “1.064- and 1.32-