Lin Yung-Hsiang, Yang Chun-Yu, Liou Jia-Hong, Yu Chin-Ping, Lin Gong-Ru
Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, No 1, Sec 4, Roosevelt Road, Taipei 106, Taiwan, China.
Opt Express. 2013 Jul 15;21(14):16763-76. doi: 10.1364/OE.21.016763.
A photonic crystal fiber (PCF) with high-quality graphene nano-particles uniformly dispersed in the hole cladding are demonstrated to passively mode-lock the erbium-doped fiber laser (EDFL) by evanescent-wave interaction. The few-layer graphene nano-particles are obtained by a stabilized electrochemical exfoliation at a threshold bias. These slowly and softly exfoliated graphene nano-particle exhibits an intense 2D band and an almost disappeared D band in the Raman scattering spectrum. The saturable phenomena of the extinction coefficient β in the cladding provides a loss modulation for the intracavity photon intensity by the evanescent-wave interaction. The evanescent-wave mode-locking scheme effectively enlarges the interaction length of saturable absorption with graphene nano-particle to provide an increasing transmittance ΔT of 5% and modulation depth of 13%. By comparing the core-wave and evanescent-wave mode-locking under the same linear transmittance, the transmittance of the graphene nano-particles on the end-face of SMF only enlarges from 0.54 to 0.578 with ΔT = 3.8% and the modulation depth of 10.8%. The evanescent wave interaction is found to be better than the traditional approach which confines the graphene nano-particles at the interface of two SMF patchcords. When enlarging the intra-cavity gain by simultaneously increasing the pumping current of 980-nm and 1480-nm pumping laser diodes (LDs) to 900 mA, the passively mode-locked EDFL shortens its pulsewidth to 650 fs and broadens its spectral linewidth to 3.92 nm. An extremely low carrier amplitude jitter (CAJ) of 1.2-1.6% is observed to confirm the stable EDFL pulse-train with the cladding graphene nano-particle based evanescent-wave mode-locking.
一种在空芯包层中均匀分散有高质量石墨烯纳米粒子的光子晶体光纤，通过倏逝波相互作用被证明可用于被动锁模掺铒光纤激光器（EDFL）。通过在阈值偏压下进行稳定的电化学剥离获得了几层石墨烯纳米粒子。这些缓慢且轻柔剥离的石墨烯纳米粒子在拉曼散射光谱中呈现出强烈的二维带和几乎消失的D带。包层中消光系数β的饱和现象通过倏逝波相互作用为腔内光子强度提供了损耗调制。倏逝波锁模方案有效地增大了与石墨烯纳米粒子的饱和吸收相互作用长度，从而提供了5%的透射率增量ΔT和13%的调制深度。通过在相同线性透射率下比较芯波锁模和倏逝波锁模，单模光纤（SMF）端面上石墨烯纳米粒子的透射率仅从0.54增大到0.578，ΔT = 3.8%，调制深度为10.8%。发现倏逝波相互作用优于将石墨烯纳米粒子限制在两根SMF跳线界面处的传统方法。当通过将980纳米和1480纳米泵浦激光二极管（LD）的泵浦电流同时增大到900毫安来增大腔内增益时，被动锁模EDFL将其脉冲宽度缩短至650飞秒，并将其光谱线宽拓宽至3.92纳米。观察到极低的载流子幅度抖动（CAJ）为1.2 - 1.6%，以确认基于包层石墨烯纳米粒子倏逝波锁模的稳定EDFL脉冲序列。
