SENSORS: The Exploration of Novel All-Purpose All-fiber Spectrometer Module for Scalable and Distributed Optical Fiber Sensor System

光纤传感器已成为结构监测中最重要的传感器之一。特别是，基于光纤布拉格光栅(FBG)的传感器与波分复用(WDM)方案结合使用，其中每个FBG传感器专用于一个传感器通道，同时共享一个公共光纤链路和询问模块，已成为实施大规模土木工程监测系统的最具吸引力的方法。FBG传感器的优势在于它的全光纤特性。它可以很容易地通过光纤链路连接到询问模块，从而绕过了劳动密集型的包装瓶颈。然而，基于FBG的传感器技术在现场部署中面临的一个主要障碍是缺乏能够处理多个FBG传感器的高性价比的询问模块。提出的全光纤光谱仪由直接在10-30厘米长的单模光纤上实现的声光可调谐滤光器(AOTF)和光纤上的半导体光电探测器组成。该光谱仪基于我们之前在可调全光纤器件方面的研究经验，用于密集波分复用光纤通信应用。它结合了全光纤器件的优点和声光可调器件的宽可调性。该全光纤光谱仪具有结构紧凑、重量轻、速度快、成本低等特点，其性能可与现有的光栅式光谱仪和法布里-珀罗光谱仪相媲美。此外，它的非阻塞特性使分布式询问体系结构能够提供可扩展性、互换性和增强的系统冗余。虽然这一建议的主要应用是结构传感，但全光纤光谱仪可以开发为用于化学和生化应用的手持式便携式传感器系统。我们方法的基本工作原理已经在实验室中得到了演示。使用频移键控(FSK)调制方案，对于1.2 nm的传感器通道间隔，我们已经证明了波长精度为0.02 nm(相当于20微应变)，并有进一步改进的空间。随着滤光片带宽的进一步减小，封装设计的改进，特别是热稳定性的提高，我们的目标是开发一台原型多截面AOTF光谱仪，在实际的土木工程结构中进行现场测试，以展示这种新方法的实用性。PI的H.P.Lee博士正在领导一个在可调谐全光纤设备方面拥有公认研究记录的团队。冯博士在探索用于土木工程结构健康监测的各种传感器方面有着杰出的研究记录。施福光博士带来了包装设计、模拟和可靠性建模方面急需的专业知识。研究基础设施已经在PI的总部机构到位，加州交通部将为其公路和桥梁的现场试验提供实物支持。拟议的项目预计将对研究、教育和潜在的技术转让产生巨大影响。从预算中可以看出，该项目严重依赖对研究生的资助。根据我们在加州大学欧文分校的经验，我们也期待本科生通过校园赞助的UROP(本科生研究机会计划)与研究生和教职员工积极参与。

Fiber-optic sensors have become one of the most important sensors for structural monitoring. Inparticular, Fiber Bragg Grating (FBG) based sensors used in conjunction with a wavelengthdivision multiplexing (WDM) scheme, where each FBG sensor is dedicated to a sensor channelwhile sharing a common fiber link and interrogation module, have emerged as the most attractiveapproach for implementing large-scale civil engineering monitoring systems. The strength of theFBG sensor lies in its all-fiber nature. It can be easily connected to the interrogation module by afiber link thus bypassing the labor-intensive packaging bottleneck. However, a major obstaclefacing FBG-based sensor technology in field deployment is the lack of a cost-effectiveinterrogation module capable of handling multiple FBG sensors.Here we propose a novel all-fiber spectrometer as the building block for a low-cost interrogationmodule. The proposed all-fiber spectrometer consists of an Acousto-Optic Tunable Filter (AOTF)implemented directly on a 10-30 cm long single-mode fiber and an on-fiber semiconductorphotodetector. The spectrometer is built on our prior research experience in tunable all-fiberdevices for dense WDM fiber-optic communication applications. It combines the merits of an all-fiberdevice and the wide tunability of an AOTF. The all-fiber spectrometer is compact, lightweight, fast, low cost and has a performance comparable to existing grating-based and Fabry-Perotspectrometers. In addition, its non-blocking characteristics enables a distributedinterrogation architecture that offers scalability, interchangeability, and enhanced systemredundancy. Although the primary application of this proposal is on structural sensing, the all-fiberspectrometer can be developed as a hand held portable sensor system for chemical andbiochemical applications.The basic operating principle of our approach has been demonstrated in the laboratory. Using afrequency-shift key (FSK) modulation scheme, we have demonstrated wavelength accuracy of0.02 nm (this corresponds to a strain of 20 ustrain) for a sensor channel spacing of 1.2 nm withroom for additional performance improvement. With further reduction of the filter bandwidth,improvement of the packaging design, particularly thermally stability, we aim at developing aprototype multi-section AOTF spectrometer to be field tested in actual civil engineeringstructures to demonstrate the practicality of this new approach.The project team reflects a multi-disciplinary effort. Dr. H. P. Lee, the PI, is leading a group witha proven research record in tunable all-fiber devices. Dr. M. Feng has a distinguished researchrecord in exploring various sensors for health monitoring of civil engineering structures. Dr. F.G.Shi brings in much needed expertise in packaging design, simulation, and reliability modeling.The research infrastructure is already in place at the PI's home institution, and the CaliforniaDepartment of Transportation will provide in-kind support for field trials on its highways andbridges.The proposed projects are expected to have strong impact on research, education, and potentialtechnology transfer. As reflected from the budget, the project is leaning heavily on supportinggraduate students. Based on our experience at UC Irvine, we also expect active participation ofundergraduate students through the campus-sponsored UROP (undergraduate researchopportunity program) to work with the graduate students and faculty.