Tailoring nonlinear interactions in highly-multimode fibers for versatile light sources

标题：基于多模产生和放大的光纤光源非技术描述：在过去的25年里，在一般的光纤领域，见证了许多令人印象深刻的进步。这些突破不仅使互联网得到了广泛的普及，而且还从根本上改变了工业制造、激光手术、光学显微镜和传感等领域。光纤激光器代表了另一个在同一时期经历了惊人增长的领域。这类激光器之所以如此成功，是因为它们具有卓越的功率可扩展性、光谱和时间的多功能性、高效率以及能够集成到强大的模块化系统中。不幸的是，就像大多数经历了能力突然进步的技术一样，用不了多久，物理限制就会出现，阻碍未来的进步。事实上，现有光纤的非线性极限和损伤阈值现在正在接近，对当前基于光纤的光源可以预期的最大脉冲能量/功率施加了限制。这项工作旨在通过利用高度多模光纤结构中非线性动力学的物理和复杂性来克服这些限制。将开发替代战略来设计新的多功能光源，这些光源在输出功率和提供的光谱密度方面比现有系统高出一个数量级。教育是这项研究工作不可或缺的组成部分。由于拟议工作的跨学科性质，参与此项目的学生将有机会体验研究中的所有步骤。这涉及到从理论模型到预期行为的实验演示再到最终产生光纤光源原型的想法。技术描述：这项研究的目标是系统地探索在当前单模方法仍需要解决方案的两个领域使用非线性多模光纤的可能性：(I)具有定制频率和模式内容的超高光谱密度、多倍频程超连续谱光源；以及(Ii)用于脉冲放大的功率可扩展、低成本的多模光纤结构。这将通过设计优先激发特定模组的策略和开发具有低差分模式增益的Yb基光纤放大器来实现。特别令人感兴趣的将是根据需要改变产生的超连续光谱，从紫外线到中红外。在这方面，将制造光子灯笼、具有适当设计的横向折射率分布的混沌光纤以及纵向变化的锥形配置，以鼓励在特定频段内产生频率。此外，还将考虑在通常色散的多模光纤中产生啁啾抛物脉冲的前景。尤其重要的是开发能够预测或解释非线性多模光纤中的过程的理论模型，例如模式凝聚，这些过程在很大程度上仍未被探索。从理论上讲，非线性和混沌之间的相互作用作为一种使超连续谱均匀化的手段仍然是一个需要研究的重要问题。容易产生混沌的纤维结构的实现为观察和研究经典混沌和波动混沌之间的复杂联系提供了一个实验平台。这些概念在光子学中的应用可以建立一种在非线性多模环境中建模和控制光传播的新范例，并将有助于开发设计新型光纤光源的替代方法。这些想法的交叉融合有望导致光子学和非线性物理学的进步。

Title: Fiber Light Sources Based on Multimode Generation and AmplificationNon-Technical Description:The past 25 years have witnessed a number of impressive advancements in the general field of fiber optics. These breakthroughs have not only enabled a widespread proliferation of the Internet, but have also radically transformed industrial manufacturing, laser surgery, optical microscopy and sensing, to mention a few. Fiber lasers represent yet another field that has experienced striking growth during this same period. What made this class of lasers so successful is their remarkable power scalability, spectral and temporal versatility, high efficiency and their ability to be integrated into robust and modular systems. Unfortunately, as with most technologies that experienced a sudden progress in capabilities, it will not be long before physical constraints appear on the horizon to dampen future progress. Indeed, nonlinear limits and damage thresholds of existing fibers are now being approached, imposing restrictions on the maximum pulse energies/power one could expect from current fiber based light sources. This work aims to overcome these limitations by exploiting the physics and complexity of nonlinear dynamics in highly multimode fiber structures. Alternative strategies are to be developed for designing new versatile light sources that outperform existing systems by orders of magnitude in terms of output power and spectral densities delivered. Education is an integral component of this research effort. Due to the interdisciplinary nature of the proposed work, the students engaged in this project will have the opportunity to experience all the steps in the research. This involves starting from ideas that originate from theoretical models to experimentally demonstrations of the anticipated behavior to finally producing a prototype fiber light source.Technical Description:The goal of this research effort is to systematically explore the possibility of using nonlinear multimode fibers in two areas where current single mode approaches are still in need of a solution: (i) ultra-high spectral density, multi-octave supercontinuum sources with customized frequency and modal content and (ii) power-scalable, low-cost multimode fiber structures for pulsed amplification. This will be accomplished by devising strategies to preferentially excite particular mode groups and by developing ytterbium-based fiber amplifiers with low differential modal gain. Of special interest will be to alter on demand the generated supercontinuum spectrum, from ultra-violet to mid-infrared. In this respect, photonic lanterns, chaotic fibers with appropriately engineered transverse index profiles, and longitudinally varying taper configurations will be fabricated to encourage frequency generation in specific bands. Moreover, the prospect for generating chirped parabolic pulses in normally dispersive multimode fibers will be considered. Of particular importance will be to develop theoretical models that can either predict or explain processes in nonlinear multimode fibers, for example mode condensation, that still remain largely unexplored. From a theoretical perspective, the interplay between nonlinearity and chaos as a means to homogenize the supercontinuum is still an important problem that will be investigated. The realization of fiber structures that are prone to chaos could provide an experimental platform that can be utilized to observe and study the intricate connection between classical and wave chaos. The use of these notions in photonics could establish a new paradigm in molding and controlling optical propagation in nonlinear multimode environments and will help develop alternative methodologies in designing novel classes of fiber-based sources. The cross-fertilization of these ideas is expected to lead to advances in both photonics and nonlinear physics.