Understanding noise and coherence properties of supercontinuum generation in non-instantaneous liquid core fibers

超连续谱产生(SCG)允许通过非线性光学效应在定义的光谱域中分配电磁能量。一种特别有效的方案依赖于高阶孤子在光纤中分裂成与色散波发射相关的基态孤子。由于SCG起源于非线性材料响应，因此它对相位和幅度噪声具有相对较高的敏感性。这种敏感性在所产生的光谱集合中强加了变化，这对于需要使用单独光谱的应用是有害的。这就需要研究产生的光谱之间的相关性，即SCG过程的相干性。在固体玻璃光纤中，对于更高的峰值功率或更长的脉冲，SCG从高度相干状态演化到非相干态，这导致了通过孤子数来定义相干极限。这一极限基本上与固体玻璃材料的瞬时时间响应有关。在先前的项目中，第一个证据表明，有液芯的光纤可以在孤子数下实现高度相干的单光子晶体，只有固体玻璃系统才能提供非相干光谱。这一改进与液芯非线性响应的非瞬时贡献有关，该非瞬时贡献是由完全由液体环境引起的且不存在于固体材料中的分子过程引起的。该项目的主要目的是了解非瞬时贡献对液芯光纤中产生的超连续谱的相干特性的影响。该项目的目标是从理论和特别是从实验的角度研究产生的光谱集合内的噪声和一阶相关程度。具体的科学问题是，例如，混合时间响应对孤子裂变和色散波形成的影响，以及这些是否有效地描述了相应的物理学。另一个问题是目前使用的相干限制，最初的迹象表明，液芯光纤的概念允许突破这一限制，在更高的输入功率水平提供相干SCG。总体而言，该项目旨在展示与基于孤子的SCG的相干性有关的新的非线性物理，该光孤子基于包含混合时间响应函数的波导平台，这与需要单独光谱的应用高度相关。

Supercontinuum generation (SCG) allows distributing electromagnetic energy via nonlinear optical effects across defined spectral domains. One particular effective scheme relies on the fission of higher-order solitons into their fundamental counterparts within optical fibers being associated with the emission of dispersive waves. Since SCG originates from nonlinear material responses, it reveals a comparably high susceptibility to phase and amplitude noise. This susceptibility imposes variations within the ensemble of generated spectra, which can be detrimental for applications requiring using individual spectra. This forms a demand for studying the correlation between generated spectra, i.e., the coherence of the SCG process. Within solid glass fibers SCG evolves from a highly coherent into an incoherent state for higher peak powers or longer pulses, having led to the definition of the coherence limit via the soliton number. This limit is fundamentally associated with the instantaneous temporal response of solid glass materials. Within the preceding project first evidence that fibers with liquid cores allow for highly coherent SCG at soliton numbers solely solid glass systems deliver incoherent spectra was found in simulations. This improvement is associated with the non-instantaneous contribution to the nonlinear response of the liquid core, resulting from molecular processes that are solely due to the liquid environment and do not exist in solid materials.The main objective of the proposed project is to understand the impact of a non-instantaneous contribution to the nonlinear temporal response on the coherence properties of supercontinua generated in liquid core fibers. The project targets investigating noise and first-order degree of correlation within the ensemble of generated spectra both from the theoretical as well as in particular from the experimental perspective. Specific scientific questions are for instance the impact of a hybrid temporal response on soliton fission and dispersive wave formation and if these are valid descriptions of the corresponding physics. Another issue is the currently used coherence limit, with first indications suggesting that the liquid core fiber concept allows breaking through that limit, providing coherent SCG at higher input power levels. Overall, the project aims to demonstrate new nonlinear physics with respect to the coherence of soliton-based SCG based on a waveguide platform incorporating a hybrid temporal response function, which is highly relevant for applications that demand individual spectra.