The Fundamental Limit of Fiber-Optic Sensors in the Infrasonic Region

摘要标题：光纤传感器在次声领域的基本限制非技术性：光纤传感器已广泛应用于工业和研究。然而，它们的基本特性之一，灵敏度的固有极限，尚未完全理解。具体地说，在次声频率（低于20 Hz），没有直接观察到光纤传感器中的固有噪声，现有的理论仍然没有定论。该项目旨在通过设计一系列实验来探测光纤中的灵敏度限制噪声，并通过先进的理论建模支持实验研究来解决这个问题。通过揭示低频传感器性能极限的物理基础，该研究将大大加深对次声光纤传感的理解，使未来的传感器设计人员能够以前所未有的灵敏度充分利用光纤传感器的潜力。此外，实验中使用的新型传感器设计将作为未来超灵敏分布式次声传感器的蓝图，这些传感器对于监测大规模杀伤性武器，地震，火山爆发，冰川运动等至关重要该项目将直接资助本科和研究生水平的多名学生，并将为大学和高中生提供顶峰和夏季研究机会。这也将有助于在亨茨维尔的亚拉巴马大学创建一个新的研究方向，即精确光纤传感，并提高NSF在亚拉巴马州的存在。技术：计划研究的首要目标是了解在低频设置光纤传感器灵敏度极限的物理学。这项研究将主要集中在直接测量的自发热噪声产生的光纤在次声区。一个平行的努力也将致力于开发一个三维粘弹性模型与同心结构来描述在光纤中的热机械噪声。为了解决在次声频率下测量微小热噪声所面临的挑战，将采用基于Mach-Zehnder-Fabry-Perot混合干涉仪的新传感器设计。初步的理论分析表明，这种方案能够将传感器灵敏度提高104倍，从而将热噪声占主导地位的频谱区域扩展到远低于1 Hz。这项研究的科学价值在于其主要目标是揭示光纤热噪声的基本物理规律。光纤热噪声的1/f特性之谜困扰了研究人员二十年。光纤传感器领域迫切需要专门针对热噪声的低频特性进行彻底的调查。通过利用混合干涉仪等新的传感概念，拟议的工作将彻底改变低频信号的光学传感，并开辟次声技术的新范式。

Abstract Title: The Fundamental Limit of Fiber-Optic Sensors in the Infrasonic RegionNontechnical: Fiber-optic sensors have been widely used in industry and research. However, one of their fundamental properties, the intrinsic limit of sensitivity, has not been fully understood. Specifically, at infrasonic frequencies (below 20 Hz), there has been no direct observation of the inherent noise in fiber-optic sensors, and the available theories remain inconclusive. The proposed project aims to address this problem by devising a set of experiments to probe the sensitivity-limiting noise in optical fibers and supporting the experimental study with advanced theoretical modeling. By uncovering the physics underlying the ultimate limit of sensor performance at low frequencies, the research will substantially deepen the understanding of infrasonic fiber-optic sensing, allowing future sensor designers to exploit the full potential of fiber-optic sensors at an unprecedented level of sensitivity. Moreover, the novel sensor designs used in the experiments will serve as blueprints for future ultra-sensitive distributed infrasound sensors, which are critical for monitoring mass-destruction weapons, earthquakes, volcanic eruptions, glacial motions, etc. The project will directly fund multiple students at both undergraduate and graduate levels and will generate capstone and summer research opportunities for college and high school students. It will also help create a new research thrust, precision fiber-optic sensing, at the University of Alabama in Huntsville, and improve the presence of NSF in the state of Alabama.Technical: The overarching goal of the planned research is to understand the physics that sets the ultimate limit of fiber sensor sensitivity at low frequencies. The investigation will primarily focus on direct measurement of the spontaneous thermal noise generated by optical fibers in the infrasonic region. A parallel effort will also be dedicated to the development of a three-dimensional visco-elastic model with concentric structures to describe the thermomechanical noise in optical fibers. To address the challenges facing the measurement of the minuscule thermal noise at infrasonic frequencies, a new sensor design based on a Mach-Zehnder-Fabry-Perot hybrid interferometer will be employed. Preliminary theoretical analysis has shown that such a scheme is able to raise the sensor sensitivity by a factor of 104, hence extending the thermal noise-dominated spectral region to well below 1 Hz. The scientific merit of the proposed research rests upon its primary goal toward uncovering the fundamental physical law of fiber thermal noise. The mystery surrounding the 1/f behavior of fiber thermal noise has puzzled researchers for two decades. There is an urgent need within the fiber-optic sensor community for a thorough investigation specifically targeting the low-frequency characteristics of thermal noise. By leveraging new sensing concepts such as hybrid interferometers, the proposed work will completely transform optical sensing for low-frequency signals and open up a new paradigm of infrasonic technologies.