玻璃纖衣單模態釔鋁石榴石晶體光纖的研製

The Research and Development of Glass-Cladding Single-Mode YAG Crystal Fiber

徐雅芹(Ya-Qin Xu)

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/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01338

摘要

單模態光纖是許多應用方面的關鍵元件，例如大增益主動元件、高效率雷射和高亮度光源。對於光纖放大器而言，單模態傳輸是一個重要的方式可以避免增益之競爭。因此，為了得到在特定波長更大的增益，我們研發單模摻鉻釔鋁石榴石晶體光纖，以為下世代之光纖通訊架構提供1000-1600 nm的光纖放大器。
實驗製造出高濃度的玻璃包覆摻鉻釔鋁石榴石晶體光纖，在單纖衣的情況下鉻離子的濃度增加至1.023×〖10〗^24 m^(-3)，相對於之前的結果提升3倍多的濃度大小。透過模擬，普通情形下，當光纖長度為4.5 cm，纖心直徑為25 µm，幫浦功率為450 mW時，可得最大增益為1.69 dB；在優化模型中，光纖長度為10 cm，纖心直徑為20 µm，鉻離子的濃度為2×〖10〗^24 m^(-3)，幫浦功率為 20 W時，可達之最大增益提升為23.43 dB。增益飽和信號功率約為7 dBm。
本實驗室採用雷射加熱基座生長法生長單晶纖心，並藉由提拉雷射加熱基座生長法進行玻璃包覆。為了減少模態數量，我們採用德國Schott公司生產的高折射率玻璃N-LasF9當做纖衣材料進行包覆，成功地製造出了單模純釔鋁石榴石晶體光纖。透過2 ~ 50 mm/min的包覆速度，N-LaSF9纖衣包覆的純釔鋁石榴石晶體光纖的截止波長可以在1381 nm至941 nm的範圍內被調變，在包覆速度大於10 mm/min時，其折射率恰好低於晶體纖心，波長1064 nm之光開始可以在N-LaSF9包覆之純釔鋁石榴石晶體光纖中傳輸。採用50 mm/min的包覆速度時可以使高折射率玻璃N-LaSF9之折射率下降至多達0.009。我們模擬出一個與LHPG製程相匹配，纖心直徑為12 µm，包覆速度為13 mm/min的N-LaSF9包覆的釔鋁石榴石晶體光纖，能夠在整個螢光波段單模態傳輸。此外，我們設計並製作出一根在大於1400 nm時會單模態導光的N-LaSF9纖衣純釔鋁石榴石光纖，並且觀察到其近場模態。

關鍵字

單模態 ； N-LaSF9纖衣 ； 釔鋁石榴石 ； 晶體光纖 ； 光纖放大器

並列摘要

Single-mode fibers are the key components in applications such as high gain active component, high efficient laser and high brightness light source. As for fiber amplifier, single-mode propagating is an essential way to get rid of the impact from gain competing. Thus in order to get larger gain at a typical wavelength, single mode Cr4+:YAG crystal fiber need to be developed.
High concentration glass-cladding Cr4+:YAG crystal fibers were made. The concentration of Cr4+ ions was increased to 1.023×〖10〗^24 m^(-3), improving more than 3 times compared to previous fibers. Within a normal case, fiber length of 4.5 cm, core diameter of 25 µm and a maximum pump power of 450 mW, a maximum gain of 1.69 dB can be get. The improved model is fiber length of 10 cm, core diameter of 20 µm Cr4+ concentration of 2×〖10〗^24 m^(-3) and pump power of 20 W, in which the gain can be improved to 23.43 dB. The gain saturation signal power is about 7 dBm.
A single-mode pure YAG crystal fiber was successfully fabricated. The cores of crystal fibers were grown by laser-heated pedestal growth (LHPG) method, and the cladding made of glass by the co-drawing LHPG process. The high-refractive index glass, N-LasF9 from Schott has been chosen as the most proper cladding material to decrease the transverse mode numbers. The cut-off wavelength of this N-LaSF9-cladding pure YAG SCCF can be tuned from 1381 to 941 nm by varying the cladding co-drawing speed from 2 to 50 mm/min in the CD-LHPG process. With a cladding speed larger than 10 mm/min, an N-LaSF9-cladding pure YAG SCCF begins to guide at 1064 nm. The maximum refractive index drop of N-LaSF9 glass cladding induced by the LHPG process can reach about 0.009 with the cladding speed of 50 mm/min. Corresponding to our LHPG fabrication process, a 12-µm core diameter and a cladding speed of 13 mm/min is needed to develop an N-LaSF9-cladding YAG fiber which is single-mode guiding at the whole emission bandwidth. In addition, the mode pattern of an N-LaSF9-cladding YAG fiber which is designed to be single-mode guiding beyond 1400 nm is fabricated.

並列關鍵字

single mode ； N-LaSF9 cladding ； YAG ； crystal fiber ； fiber amplifier

參考文獻

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