Longitudinally thickness-controlled nanofilms on exposed core fibres enabling spectrally flattened supercontinuum generation-猫眼课题宝

DOI：

10.37188/lam.2021.021

发表时间：

2021

期刊：

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通讯作者：

中科院分区：

其他

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作者：

Tilman A. K. Lühder;H. Schneidewind;Erik P. Schartner;Heike Ebendorf-Heidepriem;M. A. Schmidt

非线性频率转换是解锁未发现的物理学并为光谱学或医学实现定制光源的途径。一个关键的挑战是建立光谱平坦的输出，这在低泵浦能量下基于孤子的光转换的背景下要求特别高。在这里，我们引入了通过纵向变化谐振控制非线性频率转换的概念，允许孤子动力学的整形并实现具有相当大的光谱平坦度的宽带光谱。纵向变化的共振是通过位于先进微结构纤维核心上的厚度逐渐变化的纳米膜实现的。具有工程厚度分布的纳米薄膜是通过倾斜沉积制造的，代表了一种与波导兼容的纳米制造方法，并在系统中引入良好控制的共振，从而实现沿光纤长度的独特色散控制。通过实验检查了关键特征和依赖性，显示通过多个色散波生成和色散辅助孤子拉曼位移改善了带宽和光谱平坦度，同时在模拟中保持出色的脉冲间稳定性和相干性，这表明我们的发现与基础科学以及定制光源的相关性。简介具有特定光谱特性的宽带非线性光源对于计量、光学相干断层扫描和光谱学等许多应用至关重要。在非线性频率转换的背景下，一种成功的方法是基于孤子的超连续谱产生（SCG），它依赖于高阶孤子的裂变和相关的色散波（DW）发射。由于光/物质相互作用长度长且模式限制强，这种 SCG 方案在波导中非常有效，特别是在光纤中。它在很大程度上依赖于底层波导的色散特性，这提出了一种通过波导工程定制光生成过程的途径。当前超连续谱 (SC) 研究中的一项重要挑战是设计具有平坦输出光谱的基于超快孤子的光源，即在定义的光谱间隔内具有平坦的功率谱密度。例如，为了在光学相干断层扫描中提供高质量的点扩散函数，以及与现代重型实验室设备相比无法提供高动态范围的手持式光谱设备，需要光谱平坦度。使用长脉冲长度或高脉冲能量是通过调制不稳定性获得平坦宽带光谱的另一种方法。然而，这与输出频谱的脉冲间波动以及相关的相干性损失直接相关。在此，一位有前途的通讯作者：Markus Schmidt (markus-alexander.schmidt@uni-jena.de) 莱布尼茨光子技术研究所，Albert-Einstein-Str。 9, 07745 德国耶拿物理科学学院和 ARC 纳米生物光子学卓越中心 (CNBP) 和光子学和高级传感研究所 (IPAS)，阿德莱德大学，阿德莱德 SA 5005，澳大利亚奥托肖特材料研究所，Fraunhoferstr. 9, 07745 Jena, 德国6, 07743 Jena, 德国阿贝光子与物理学院，弗里德里希席勒大学，07743 Jena, 德国在不使用调制不稳定性的情况下以低输入能量对输出进行光谱均匀化的途径依赖于通过沿其轴几何改变波导横截面来纵向调制波导的色散，从而导致诸如多重DW发射之类的效应。两者均逐步级联，通过拼接光纤部分谨慎地改变色散分布；此外，在锥形光子等系统中已经实现了连续（平滑）变化的色散景观。 © 作者 2021 开放获取本文已根据知识共享署名 4.0 国际许可证获得许可，允许使用、共享、改编、分发和复制。在任何媒介或格式中，只要您对原作者和来源给予适当的认可，提供知识共享许可的链接，并注明是否进行了更改。本文中的图像或其他第三方材料包含在文章的知识共享许可中，除非材料的出处另有说明。如果文章的知识共享许可中未包含材料，并且您的预期用途不受法律法规允许或超出允许的用途，则将直接从版权所有者获得许可。要查看此许可证的副本，请访问 http://creativecommons.org/licenses/by/4.0/ 接受文章预览

Nonlinear frequency conversion is a pathway to unlock undiscovered physics and implement tailored light sources for spectroscopy or medicine. A key challenge is the establishment of spectrally flat outputs, which is particularly demanding in the context of soliton-based light conversion at low pump energy. Here, we introduce the concept of controlling nonlinear frequency conversion by longitudinally varying resonances, allowing the shaping of soliton dynamics and achieving broadband spectra with substantial spectral flatness. Longitudinally varying resonances are realised by nanofilms with gradually changing thicknesses located on the core of an advanced microstructured fibre. Nanofilms with engineered thickness profiles are fabricated by tilted deposition, representing a waveguide-compatible approach to nano-fabrication, and inducing wellcontrolled resonances into the system, allowing unique dispersion control along the fibre length. Key features and dependencies are examined experimentally, showing improved bandwidth and spectral flatness via multiple dispersive wave generation and dispersion-assisted soliton Raman shifts while maintaining excellent pulse-to-pulse stability and coherence in simulations, suggesting the relevance of our findings for basic science as well as tailored light sources. Introduction Broadband nonlinear light sources with specific spectral properties are essential for many applications such as metrology, optical coherence tomography, and spectroscopy. Within the context of nonlinear frequency conversion, one successful approach is the soliton-based supercontinuum generation (SCG), which relies on the fission of higher-order solitons and the associated emission of dispersive waves (DWs). Because of the long light/matter interaction lengths and strong mode confinement, this SCG scheme is highly effective in waveguides, particularly in optical fibres. It relies heavily on the dispersive properties of the underlying waveguide, suggesting a pathway for tailoring the light generation process through waveguide engineering. One essential challenge in current supercontinuum (SC) research is the design of ultrafast soliton-based sources with a flat output spectrum, that is, with a flat power spectral density across defined spectral intervals. Spectral flatness is required, for example, to provide high quality point spread functions in optical coherence tomography and for handheld spectroscopic devices that cannot provide high dynamic ranges compared to modern heavy laboratory equipment. Using long pulse lengths or high pulse energies is an alternative method to obtain flat broadband spectra through modulation instability. However, this is directly associated with the pulse-to-pulse fluctuations of the output spectrum and the associated loss of coherence. Here, one promising Correspondence: Markus Schmidt (markus-alexander.schmidt@uni-jena.de) Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany School of Physical Sciences and ARC Centre of Excellence for Nanoscale BioPhotonics (CNBP) and Institute for Photonics and Advanced Sensing (IPAS), The University of Adelaide, Adelaide SA 5005, Australia Otto Schott Institute of Material Research, Fraunhoferstr. 6, 07743 Jena, Germany Abbe School of Photonics and Physics Faculty, Friedrich Schiller University, 07743 Jena, Germany pathway to spectrally homogenise the output at low input energy without using modulation instability relies on longitudinally modulating the dispersion of the waveguide by geometrically changing the waveguide cross section along its axis, leading to effects such as multiple DW emission. Both cascaded step-wise, discreetly changing the dispersion profiles via spliced fibre sections; furthermore, continuously (smoothly) varying dispersion landscapes have been realised in systems such as tapered photonic © The Author(s) 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution, and reproduction. in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, permission will be obtained directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ ACCEPTED ARTICLE PREVIEW

Longitudinally thickness-controlled nanofilms on exposed core fibres enabling spectrally flattened supercontinuum generation

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