Thakur Siddharatha, Semnani Behrooz, Safavi-Naeini Safieddin, Majedi Amir Hamed
Department of Electrical & Computer Engineering, University of Waterloo, Waterloo, N2L3G1, Canada.
Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, N2L3G1, Canada.
Sci Rep. 2019 Jul 22;9(1):10540. doi: 10.1038/s41598-019-46710-x.
Graphene's giant nonlinear optical response along with its integrability has made it a vaunted material for on-chip photonics. Despite a multitude of studies confirming its strong nonlinearity, there is a lack of reports examining the fundamental processes that govern the response. Addressing this gap in knowledge we analyse the role of experimental parameters by systematically measuring the near-infrared spectral dependence, the sub-picosecond temporal evolution and pulse-width dependence of the effective Kerr coefficient (n,) of graphene in hundreds of femtosecond regime. The spectral dependence measured using the Z-scan technique is corroborated by a density matrix quantum theory formulation to extract a n, ∝ λ dependence. The temporal evolution obtained using the time-resolved Z-scan measurement shows the nonlinearity peaking at zero delay time and relaxing on a time-scale of carrier relaxation. The dependence of the n, on pulse duration is obtained by expanding the input pulse using a prism-pair set-up. Our results provide an avenue for controllable tunability of the nonlinear response in graphene, which is limited in silicon photonics.
石墨烯巨大的非线性光学响应及其可积性使其成为片上光子学中备受赞誉的材料。尽管众多研究证实了其强烈的非线性，但缺乏对支配该响应的基本过程的研究报告。为填补这一知识空白，我们通过系统测量石墨烯在数百飞秒 regime 下有效克尔系数（n,）的近红外光谱依赖性、亚皮秒时间演化和脉冲宽度依赖性，来分析实验参数的作用。使用Z扫描技术测量的光谱依赖性通过密度矩阵量子理论公式得到证实，以提取n, ∝ λ依赖性。使用时间分辨Z扫描测量获得的时间演化表明，非线性在零延迟时间达到峰值，并在载流子弛豫的时间尺度上弛豫。通过使用棱镜对装置扩展输入脉冲来获得n, 对脉冲持续时间的依赖性。我们的结果为石墨烯中非线性响应的可控可调性提供了一条途径，而这在硅光子学中是有限的。
