Jiang Yuyuan, Zhou Jian, Lou Bowen, Liu Jing, Xu Yanhua, Zhao Junqing, Li Lei, Tang Dingyuan, Shen Deyuan
Jiangsu Key Laboratory of Advanced Laser Materials and Devices, Jiangsu Collaborative Innovation Center of Advanced Laser Technology and Emerging Industry, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, Jiangsu, China.
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 637123, Singapore.
Nanophotonics. 2021 Oct 27;11(1):87-100. doi: 10.1515/nanoph-2021-0513. eCollection 2022 Jan.
Tapered fiber (TF) and D-shaped fiber (DF) are two types of widely investigated devices in facilitating evanescent-field interactions with external materials. Although they have been found to be particularly useful in various ultrafast regimes, to date there is still no clear or systematic investigation on their local nonlinearities as well as the exerted influences on ultrafast behaviors. Herein, we present such thorough investigation through local nonlinearity engineering on TF and then in contrast with a DF as a reference. Optically deposited black phosphorus quantum dots (BPQDs) are used for saturable absorption. The nanometer-scale extremely small sizes of the BPQDs helpfully eliminate size-induced uncertainties or distortions during both device fabrication and the latter light-matter interaction. For the TF, in the experiment, it is found that the local nonlinear effect starts to be rather appreciable as the TF shrinks to a moderate thickness. Remarkably in comparison, the local nonlinearity of the DF itself can even be neglected reasonably, but after coating with BPQDs, it possesses a much larger modulation depth than any of the used BPQDs-coated TFs with different thicknesses/lengths. Further, we theoretically analyze the related locally nonlinear effects and reveal, for the first time, the direct origin of saturable absorption with evanescent-field-based general structures.
锥形光纤（TF）和D形光纤（DF）是两种在促进倏逝场与外部材料相互作用方面受到广泛研究的器件。尽管它们已被发现在各种超快领域中特别有用，但迄今为止，对于它们的局部非线性以及对超快行为的影响仍没有明确或系统的研究。在此，我们通过对TF进行局部非线性工程，并与作为参考的DF进行对比，进行了如此深入的研究。光学沉积的黑磷量子点（BPQDs）用于饱和吸收。BPQDs的纳米级极小尺寸有助于消除器件制造过程中以及后续光与物质相互作用过程中尺寸引起的不确定性或失真。对于TF，在实验中发现，当TF收缩到中等厚度时，局部非线性效应开始变得相当明显。相比之下，DF本身的局部非线性甚至可以合理地忽略，但在用BPQDs包覆后，它具有比任何不同厚度/长度的BPQDs包覆的TF更大的调制深度。此外，我们从理论上分析了相关的局部非线性效应，并首次揭示了基于倏逝场的一般结构的饱和吸收的直接起源。
