基于频移干涉光纤腔衰荡的高灵敏多点式光纤磁场传感方法研究

Fiber optic magnetic field sensing technologies have become an important development tendency of magnetic field sensing technologies due to the advantages including quick response, electric insulation and anti- electromagnetic interference. However, they have many difficulties in the realization of high sensitivity, low cost or multipoint detection because of sensor structures, demodulation methods or multiplexing schemes. Continuous-wave spatial-domain frequency-shifted interferometry fiber cavity ringdown (FSI-CRD) not only has the high-sensitivity advantage of CRD techniques, but also has the advantages of high signal-to-noise ratio (SNR) and low cost of FSI. The applications of FSI-CRD in single-point chemical solution and single-point gas sensing have been well tested. Therefore, the project proposes to extend FSI-CRD to magnetic field sensing, and fuse it into the demodulating and multiplexing of the magneto-fluid-based magnetic field sensors, and realize a new highly-sensitive multipoint fiber magnetic field sensing method. The proposal focuses on carrying out the researches on the FSI-CRD fiber optic magnetic field sensing mechanism, the design of sensors and their multipoint sensing, and verifying the new method through magnetic field sensing experiments. The project uses the multiple cycle absorption of the continuous light in fiber ringdown cavity, the refractive index controllability of magneto-fluid and the high refractive index sensitivity of a micro-structure fiber to greatly improve the magnetic field sensing sensitivity, and it also utilizes the high SNR of FSI to realize the multiple-channel multiplexing. This work can be expected to obtain a new fiber optic magnetic field sensing method with high sensitivity and low cost, which has very important theoretic and practical significances.

光纤磁场传感技术因其响应快、电绝缘、抗电磁干扰等优点，已成为磁场传感技术的重要发展趋势，但受限于传感器结构、解调或者复用方法，在实现高灵敏度、低成本或者多点探测方面存在不少困难。连续波空间域频移干涉光纤腔衰荡技术既具有腔衰荡的高灵敏度优势，又具有频移干涉的高信噪比和低成本的优势，已在单点化学溶液与单点气体传感领域得到了很好的检验。本项目拟拓展其在磁场传感中的应用，提出将其融入基于磁流体的光纤磁场传感器的解调及复用中，实现高灵敏度多点式光纤磁场传感新方法。重点开展频移干涉光纤腔衰荡磁场传感机理、高灵敏度传感器设计及多点传感的研究，并通过磁场传感实验进行验证。本项目利用连续光在光纤衰荡腔中的多次循环吸收、磁流体的折射率可控性以及微结构光纤的高折射率敏感性大大提高磁场传感的灵敏度，同时利用频移干涉的高信噪比实现多通道传感器复用，有望获得高灵敏度低成本光纤磁场传感新方法，具有重要的理论和现实意义。

光纤磁场传感技术具有响应快、电绝缘、抗电磁干扰等优点，但其灵敏度、经济性或复用能力亟待进一步提高，而频移干涉光纤腔衰荡（FSI-FCRD）技术具有高灵敏度、高信噪比和低成本的独特优势。因此，本项目着重开展了基于FSI-FCRD技术的高灵敏多点式磁场传感研究。提出了基于FSI-FCRD技术和磁流体包覆边抛光纤的单点光纤磁场传感技术，测得在50 ~ 300 Gs范围内磁场的灵敏度为2.5310-3 (km-1·Gs-1)，系统的稳定性达0.146%，高于传统的时域光纤腔衰荡系统。在保持磁场强度不变的情况下，研究了磁流体的热效应对整个FSI-FCRD磁场传感系统性能的影响，表明系统在13.47 ~ 17.47℃范围内具有良好的线性响应。利用蚀刻光纤包裹磁流体和FSI-FCRD技术制成温度传感器，在-10 oC到50 oC范围内获得良好的线性响应。提出了一种基于磁流体包覆锥形光纤的FSI-FCRD多点光纤磁场传感系统，将光纤磁场传感头的温度始终保持为20 oC，进行了双通道磁场传感实验验证，在221 ~ 721Oe范围内获得的灵敏度分别为9.38×10-5和-2.28×10-5 /(km•Oe)，稳定性分别为0.02%和0.04%。结合磁流体包覆的边抛光纤，提出了一种准分布式FSI-FCRD磁场传感方法。当外加磁场由0增加到250 Oe时，两个传感单元的灵敏度分别为6.7894×10-4和7.4980×10-4dB/Oe，理论分析表明在同等实验条件下系统可以实现30个相同传感单元的复用。为了进一步验证FSI-FCRD技术在多点高灵敏度传感性能，提出了基于FSI-FCRD技术的多点应力和多点压力传感方法，实验结果表明该方案可作为一种成本低、灵敏度高、稳定性高的多功能传感技术平台。本项目取得的研究成果对于实现高灵敏度、低成本、多点式光纤磁场传感技术具有重要的理论意义和应用价值。