玻璃包覆晶體光纖之寬頻光子元件

Glass-clad crystal fiber based broadband photonic devices

鄭東祐(Dong-Yo Jheng)

指導教授 ： 黃升龍

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.00047

摘要

寬頻光源是許多應用中的關鍵元件，例如光纖通訊以及光學同調斷層掃描術。本論文展示了以玻璃包覆之晶體光纖所製成之寬頻光子元件，所使用之晶體光纖，皆先以雷射加熱基座生長法生長單晶纖心，再以共提拉雷射加熱基座生長法進行玻璃包覆。
本論文展示了利用硼矽酸玻璃包覆摻鈰釔鋁石榴石晶體光纖所製作的高亮度寬頻光源。藉由最佳化退火參數，在低泵浦功率下其量子產率接近95%。在功率為1.4瓦的藍光半導體雷射泵浦下，由直徑25微米的晶體纖心中輸出的螢光功率達到19.9毫瓦，對應的輸出亮度為每平方公釐每單位立體角30.3瓦特。此一高亮度寬頻光源適合應用在光學同調斷層掃描術。
本文中成功製作出半球形外部共振腔摻鉻釔鋁石榴石雙纖衣晶體光纖雷射，其斜線效率達到17.3%，閾值泵浦功率為56毫瓦。此外我們也建立了一套分佈式的數值模擬程式來模擬晶體光纖雷射與放大器，藉由擬合搭配不同穿透率輸出耦合透鏡的雷射效率，求得晶體光纖之傳輸損耗為每公分0.01分貝。同時我們也模擬了摻鉻釔鋁石榴石晶體光纖放大器的效能，當使用10公分長的高濃度摻鉻釔鋁石榴石晶體光纖時，得到在1431奈米波長下的峰值增益為22.7分貝。
本文中也發展出了可調波長的摻鉻釔鋁石榴石雙纖衣晶體光纖雷射，藉由旋轉準直式外部共振腔中的單片式雙折射濾波片，雷射輸出波長可由1353奈米調至1509奈米，閾值泵浦功率為70毫瓦。在調整輸出波長的過程中，也觀察到了由不同橫模干涉所導致的波長跳躍。
為了減少橫模數量與降低傳輸損耗，本文成功製作了由N-SF57與N-LaSF9兩種高折射率玻璃所包覆的少模純釔鋁石榴石晶體光纖，並對其特性進行量測。最後，我們也設計出由N-LaSF9與N-LaSF41玻璃所包覆的摻鉻釔鋁石榴石晶體光纖，可以在1到1.7微米的波長範圍內達到單一橫模導光。

關鍵字

晶體光纖 ； 寬頻光源 ； 可調波長雷射 ； 摻鉻釔鋁石榴石 ； 摻鈰釔鋁石榴石

並列摘要

Broadband light sources are the key components in applications such as the high-capacity optical communication and the optical coherence tomography. In this dissertation, broadband photonic devices based on glass-clad fibers with single-crystalline cores were demonstrated. The cores of crystal fibers were grown with the laser-heated pedestal growth (LHPG) method, and then cladded with glass using the co-drawing LHPG process.
High-brightness broadband light source was presented with the Pyrex-clad Ce3+:YAG crystal fiber pumped with a blue laser diode. By optimizing the annealing conditions, the quantum yield under low pump power was estimated to be 95%. A 19.9-mW fluorescence output from the crystal fiber core with a 25-μm diameter was achieved with a 1.4-W pump power, and the corresponding radiance was 30.3 W mm-2 sr-1. This high-brightness broadband light source is useful for the optical coherence tomography.
Hemispherical external-cavity Cr4+:YAG double-clad crystal fiber lasers have been demonstrated with a 17.3% slope efficiency and a 56-mW threshold pump power. A simulation program with distributed model for the crystal fiber laser and amplifier was developed. The propagation loss extracted by fitting the laser performances with different output couplers was 0.01 dB/cm. Performance of the Cr4+:YAG crystal fiber amplifiers were also simulated, and a 22.7-dB gain at 1431 nm can be achieved with a 10-cm crystal fiber with enhanced concentration.
Broadband tunable laser from 1353 to 1509 nm was demonstrated with the Cr4+:YAG double-clad crystal fiber. The laser output wavelength was tuned by rotating a single-plate birefringent filter within the collimated external cavity. The laser threshold was 70 mW in the presence of the birefringent filter. The wavelength tuning was discrete due to the interference between the transverse modes.
High-index-glass-clad crystal fibers have been developed for decreasing the number of transverse modes and reducing the propagation loss. Few-mode pure YAG crystal fibers cladded with N-SF57 and N-LaSF9 glasses were successfully fabricated. Finally, we also proposed designs of N-LaSF9-clad and N-LaSF41-clad Cr4+:YAG crystal fibers which can achieve single-mode guiding over the wavelength range from 1 to 1.7 μm.

並列關鍵字

crystal fiber ； broadband light source ； tunable laser ； Cr4+:YAG ； Ce3+:YAG

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