Please use this identifier to cite or link to this item:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/61890
Title: | 以電化學法慢速剝離高品質低層數石墨烯奈米片應用於摻鉺光纖雷射之被動鎖模 Fabrication of high-quality few-layer graphene nano-sheet by ultraslow electrochemical exfoliation for application in passive mode-locking of Erbium-doped fiber lasers |
Authors: | Chun-Yu Yang 楊竣宇 |
Advisor: | 林恭如 |
Keyword: | 電化學剝離,石墨烯,鎖模,摻鉺光纖雷射, Electrochemical Exfoliation,Graphene,Mode-locking,Erbium-doped Fiber Laser, |
Publication Year : | 2013 |
Degree: | 碩士 |
Abstract: | 我們成功地利用慢速電化學剝離的方法得到不需要進行後退火製成的高品質低層數石墨烯奈米片。當電解電壓從6伏特調減到3伏特,電解石墨烯之拉曼散射訊號中的D峰與G峰比值隨之減小,指出使用靠近電解閥值的電壓進行電解有效抑制了電解過程中產生的結構缺陷。另一方面,2D峰與G峰的比值也同時增大兩倍,證實利用靠近閥值的電壓進行電解能減低電解石墨烯之層數。由電解石墨烯的XPS分析也確認了在低電壓電解時陽極氧化是被抑制的。經過同樣的離心萃取條件後,電解石墨烯的平均直徑從7微米縮小到0.5微米隨著電解電壓由6伏特降低到3伏特。利用3伏特電解得到的低層數石墨烯奈米片接著被使用來進行摻鉺光纖的被動鎖模。再直接將電解製程後得到的溶液滴在光纖接頭上並進行乾燥以後,石墨烯奈米片就沾附在光纖的端面上,其數量密度為15每平方微米,石墨烯奈米片並被隨光纖一起置於總群延遲色散為-0.154平方匹秒的摻鉺光纖雷射中。被置入的石墨烯奈米片造成的線性穿透率及調變深度分別為92.5%及53%。被鎖模的摻鉺光纖則產生了脈衝寬度為454.5飛秒、波長寬度為5.6奈米的脈衝列,證實此脈衝是接近被動鎖模的轉換極限,而其輸出脈衝的重複頻率為26.7百萬赫,輸出平均功率為8.91毫瓦。利用不同電壓電解的石墨烯奈米片接著被使用作為飽和吸收體,而當電解電壓從3伏特增加到6伏特,調變深度也從53%降低到17%。在進行低增益摻鉺光纖的被動鎖模時,不同樣本的鎖模表現有明顯的差異,且與樣本調變深度有關。然而當幫浦雷射的電流從200毫安培提高到900毫安培,不同樣本的鎖模表現差異就減小了。我們利用Haus’ master equation進行數值模擬來描述摻鉺光纖中脈衝形成的過程,發現在加大增益之後,負的群延遲色散及自相位調變效應的交互作用會主導脈衝成型。在幫浦雷射的電流為900毫安培時,此摻鉺光纖雷射系統中自相位調變與群延遲色散造成的脈衝壓縮率大約為0.3。 High-quality few-layer graphene nano-sheet without the need of post annealing procedure is obtained with ultra-slow electrochemical exfoliation of graphite. A decreasing D/G Raman scattering band intensity ratio with reducing exfoliation bias from +6 to +3 volts implies suppression on the structural defect with controlling the exfoliation bias to the threshold. In contrast, the I(2D)/I(G) ratio is concurrently enlarged by twice to support the decrease in layer number of exfoliated graphene nano-sheets with exfoliation bias lowered to the threshold. The X-ray photoelectron spectroscopy also confirms the suppression of the anode oxidation in the few-layer graphene nano-sheets with low exfoliation bias. After extracting by centrifugation, the average diameter of the exfoliated graphene nano-sheets extracted from the acetone solution is ranged from 7 um to 0.5 um as the exfoliation bias decreasing from 6 to 3 volts. The few-layer graphene nano-sheets electrochemically exfoliated at 3 volt is then demonstrated to passively mode-lock the erbium-doped fiber lasers. By spreading and drying the aqueous solution, the graphene nano-sheets are directly imprinted onto the connector end-face of a single-mode fiber patchcord inside the erbium-doped fiber laser (EDFL) ring cavity with the total GDD of -0.154 ps2. The linear transmittance and modulation depth of the inserted graphene nano-sheets are respectively 92.5% and 53%. The mode-locked EDFL can deliver a pulse-train with a pulsewidth of 454.5 fs and a bandwidth of 5.6 nm, at a repetition rate of 26.7 MHz and an average output power of 8.91 mW. The time-bandwidth product of 0.32 is close to the transform limit. The graphene nano-sheets exfoliated under different biases are next employed as saturable absorbers, and the modulation depth is decreased from 53% to 17% with the exfoliation bias increased from 3 to 6 volts. As being used to passively mode-lock the EDFLs at low gain condition, the different samples show clearly distinct mode-locking performances which is related to the modulation depth. However, such divergence is attenuated when the currents of the pumping laser diodes increased from 200 to 900 mA. The numerical simulation by using Haus’ mater equation is employed to describe the EDFL pulse formation, and the interaction between the anomalous GDD and the SPM effects is investigated to become the dominating mechanism with the increasing gain. The compression ratio with the cooperation of SPM and GDD effects is about 0.3 under the pumping currents of two laser diodes of 900 mA. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/61890 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 光電工程學研究所 |
Files in This Item:
File | Size | Format | |
---|---|---|---|
ntu-102-1.pdf Restricted Access | 6.3 MB | Adobe PDF |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.