以奈米碳粉/石墨/石墨烯為飽和吸收體之 被動鎖模摻鉺光纖雷射

Abstract

我們首先使用碳系材料奈米粒子作為被動鎖模摻鉺光纖雷射中的飽和吸收體，其中包括石墨奈米粒子、炭粉奈米粒子與碳黑奈米粒子等。我們以研磨塊材的方式製作奈米粒子，再將奈米粒子直接塗抹於單模光纖端面上，即可將此飽和吸收體置入於雷射共振腔內，藉此產生被動鎖模摻鉺光纖雷射。初期，我們使用石墨奈米粒子搭配此種簡易的方法，只可產生皮秒級被動鎖模摻鉺光纖雷射。這是由於摻鉺光纖放大器的增益過小，以及石墨奈米粒子因自我聚集的效應而增大其體積，使得飽和吸收過大。因此，我們製作一高增益之摻鉺光纖雷射，並發明依簡易之塗抹-擦拭-剝落法以降低石墨奈米粒子之體積(或層數)。藉此，我們能將此類鎖模雷射之脈衝壓縮至375 fs。此外，我們以拉曼光譜、X射線繞射光譜、與X射線光電子光譜進行奈米材笑之光電特性量射，並使用一脈衝雷射測量其非線性吸收特性。我們也使用理論模擬詳細地分析雷射動態行為。之後，我們也使用其他碳矽材料奈米粒子作為飽和吸收體，並以上述優化之方法，成功地獲得百飛級被動鎖模摻鉺光纖雷射。藉由理論分析，我們發現在高功率增益的操作之下，雷射環腔內會產生極高的自相位調變效應。如果此效應能與群速度延遲色散效應互相補償，即可進一步地壓縮脈衝寬度。我們也嘗試將石磨奈米粒子虹吸於光子晶體光纖中，以產生被動鎖模摻鉺光纖雷射。為了獲得小尺寸且體積均勻之石磨奈米粒子，我們使用一化學電解法製作石墨奈米粒子。使用此漸消波反應方法 能提高非線性反應長度 並可避免因腔內光束直接穿透而破壞飽和吸收體。

The nano-scale carbon based materials are firstly demonstrated to be the saturable absorbers for passively mode-locked EDFLs, including graphite nano-particle, charcoal nano-particle and carbon black nano-particle. The structural properties of the nano-particles are investigated by Raman scattering spectroscopy, XRD and XPS. In the first stage, the passively mode-locked EDFL with graphite nano-particles can only generate the ps-degree pulsewidth. After the cavity gain is enhanced by a high-gain EDFA, and the particle size (or layer number) is reduced by using an imprting-exfoliation-wiping method, the pulsewidth can be compressed to 375 fs. The cooperation of GDD and SPM effects has a great impact on the pulse formation than the SAM effect of saturable absorber. In this condition, the pulse can be further compressed by the cooperation of GDD and SPM effects. After the investigation of graphite nano-particle, the passively mode-locked EDFL with charcoal nano-partilce is also improved to hundreds fs-degree. Although the mode-locking ability of each carbon based material is different, however, with the favor of negative GDD and strong SPM, the hundreds fs-degree passively mode-locked EDFLs can be obtained. The evanescent wave interaction of saturable absorber is employed to produce the passively mode-locked EDFL. The electrochemically exfoliated graphite nano-particles are siphoned into the photonic crystal fiber to induce the evanescent wave interaction. By using this method, the damage of saturable absorber under high intracavity power operation can be avioded, and the nonlinear interaction can be also lengthened.