基于傅立叶域锁模激光的宽频带分布式微结构光纤声波传感机理研究

Oriented to the vast sea area, long-haul distributed acoustic-wave sensing is characterized by great significance of scientific research and practical applications for both exploring the marine science and monitoring the marine safety. Conventional distributed sensing technologies are principally based on the serial processing approach of the backscattering light in standard single-mode fibers (SMF). And the low signal to noise ratio (SNR) of the probe signal leads to a degraded measurement precision and limits the response speed, which seriously hinders the broadband acoustic-wave detection under a long sensing distance. To solve the aforementioned technical problems, the project creatively proposes the research on broadband and distributed microstructure-fiber acoustic-wave sensing assisted with spectrum-limited Fourier domain mode-locked (FDML) laser. Aiming at the systematic study from mechanism, technologies, devices, methods to platforms, the research mainly develops the following five contents: scattering-enhancement mechanism of the local micro-structured spots in sensing fiber, design and fabrication of the continuous-distributed multi-band micro-structured fiber, generation mechanism of the spectrum-limited FDML laser, self-reference phase-extraction method of the coherent detection, and construction of the broadband distributed fiber acoustic-wave sensing system. Significantly, by clarifying these three scientific issues, including scattering enhancement of the distributed sensing fiber, generation of the chirp-controlled and high-coherent lasing signal, and denoising effect for the ultra-low-frequency acoustic-wave detection, this project would break through the responsive bandwidth limitation induced by the low-frequency noise and long-haul sensing, which could further facilitate the establishment of the theory framework and experimental platform of the long-haul, broadband and high-precision distributed acoustic-wave sensing system.

我国海域面积辽阔，长距离分布式声波探测在海洋科学探索及海洋安全监测中具有重要的科学意义和应用价值。传统的分布式传感技术主要基于普通光纤中低信噪比后向散射光的串行处理机制，因此测量精度低、响应速度慢，无法满足长距离情况下的宽频带声波探测需求。针对这一技术难题，本项目创新性地提出基于谱受限傅立叶域锁模激光的宽频带分布式微结构光纤声波传感机理。从机理、工艺、器件、方法和平台等方面展开系统研究，主要包括传感光纤局域微结构点散射增效机理、多波段连续分布式微结构光纤设计与制备、谱受限傅立叶域锁模激光产生机制、相干探测自参考相位提取方法及宽频带分布式光纤声波探测系统等研究内容，重点解决分布式传感光纤散射增效，啁啾可控高相干激光信号产生及超低频声波探测消噪等关键科学问题，突破低频噪声和高频频带的限制，最终实现长距离、宽频带、高精度分布式声波探测技术的理论体系和实验平台。

深海战略是国家重大战略需求，实现“透明海洋”是海洋资源开发利用、监控海洋安全的重要技术前提，光纤分布式水听技术是近年来水下声场探测的研究热点。本项目针对长距离分布式声波传感（DAS）中存在的水声探测灵敏度低、次声频段探测噪声大、高频探测频带受限的瓶颈问题，提出新型的离散散射增强微结构光纤（DSE-MOF）作为传感载体，基于此开展微结构光纤DAS机理及试验研究，经过四年技术攻关，形成了从“光纤—算法—系统—应用”的系统性工作。研究突破 主要包括：从材料、工艺等方面攻克了紫外透明涂层光纤及DSE-MOF的工业化在线制备难题，打破国外技术垄断；建立了完善的DSE-MOF DAS传感理论，创新性地提出基于参考链路和LS-SVM机器学习辅助的低频探测噪声抑制技术，以及基于微结构光纤时隙分插复用的响应扩频技术，刷新了光纤DAS技术的探测性能极限；研制了高灵敏、宽频带、长距离光纤DAS设备样机，以及基于双重增敏机制的轻量化、超细径、全分布水听拖曳光缆，支持DSE-MOF长度突破100km，声波响应频带覆盖0.001Hz~300kHz，最小可测应变小于5pε/√Hz，水听拖曳光缆直径20mm，水声灵敏度优于-137dB re rad/μPa；已在千岛湖、木兰湖等地进行了现场测试，成功探测到水下主被动目标，展现出极具竞争力的应用性能。该项目成果实现了一种全新的水下探测手段，具有大范围、高灵敏、宽频带、无盲区、易布放等显著优势，能够为海洋科学探索及海洋安全监测提供创新的科学研究手段。. 项目研究成果在OEA、JLT等国内外高水平期刊和OFC、CLEO等高水平国际会议上发表学术论文22篇，其中SCI收录论文11篇；受邀在国内外学术会议做大会和特邀报告12次，撰写特邀论文1篇，出版2本英文学术专著的章节；申请发明专利13项，9项已获授权，核心专利技术以许可使用方式获得转化收益120万元；获得中国安全生产协会安全科技进步二等奖、湖北省技术发明二等奖各1项；项目负责人先后获得国家优青、湖北省创新群体等项目支持；培养博士、硕士研究生8人。

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