基于频率分裂与偏振效应的超高分辨率光纤光栅静态应变检测关键技术研究

The latest research shows that the nano-resolution fiber Bragg grating static strain measurement has an important application value in the field of crustal deformation observation. Due to the relatively wide FWHM bandwidth of fiber grating, the wavelength nonlinearity in the wavelength swept laser and the temperature compensation inaccuracy of the reference grating, it’s difficult to further improve the static strain resolution of the system. The aim of the project is to solve the problems above. The erbium doped active phase shifted grating is used in the project to monitor static strain and temperature. By using the dual polarization effect and combination of the power control technology of pump laser and high-resolution beat frequency signal detection technology, a set of high-resolution static strain and temperature response will be recorded. In addition, a circle interrogation loop will be designed for the phase shift grating. In the loop, using the frequency division character of the phase shift grating, a set of ultra narrow bandwidth high reflection spectrum will be received. Then peak searching technology of one-sided frequency swept laser is used to solve the wavelength scanning nonlinearity problem and another data set of high-resolution static strain and temperature response will be obtained. At last, using the second order matrix method to analyze the two data, the high precision self temperature compensation will be realized. Therefore, an ultra-high-resolution static strain measurement is achieved. Through the research of the project, a long-term ultra-high-resolution static strain of 0.1 nε level will be realized, which is of great significance to promote the practical application of fiber optic sensors in crustal deformation observation.

最新研究表明，高分辨率（nε量级）光纤光栅静态应变检测技术在地壳形变观测领域具有重要应用价值。但受限于光纤光栅的半高带宽、扫频激光器的波长扫描非线性、以及参考光栅的温度补偿精度等问题，进一步提高系统的静态应变测量分辨率成为了该领域急需解决的关键技术问题。本项目，首先采用有源相移光栅作为静态应变、温度传感元件，利用其双偏振效应，结合泵浦功率控制与高分辨率拍频信号检测技术，得到一组高分辨率静态应变、温度响应。其次，对该相移光栅设计一种环形询问光路，利用其频率分裂特性，得到一组超窄半高带宽的反射谱；再采用单边带扫频激光寻峰技术，解决波长扫描非线性问题，并得到另一组高分辨率静态应变、温度响应；最后，利用二阶矩阵法实现相移光栅的高精度温度自补偿和超高分辨率静态应变检测。通过本项目的研究，有望实现0.1 nε量级的超高分辨率光纤光栅静态应变测量，对促进光纤传感器在地壳形变观测中的应用具有重要研究意义。

光纤光栅由于具有本质无源、耐极限环境等优势，是地壳形变观测和地震监测领域的重要发展方向。本项目面向地壳形变观测开展超高分辨率光纤光栅静态应变检测关键技术研究，主要包括超高分辨率光纤光栅或有源相移光栅（光纤激光器）静态应变询问光路、高分辨率拍频频率解调技术、高精度光纤光栅波长差解调算法等三个方面的研究内容。本项目的主要成果如下：.（1）静态应变询问光路设计与解调技术研究方面.① 提出基于激光锁频和拍频解调的超高分辨率有源相移光栅静态应变解调技术，十分钟内的静态信号解调精度达到0.14 nε，达到国际先进水平。.② 发展了一种基于光纤光栅有效腔长的超高精度光纤温度传感技术，直接利用光纤光栅谐振腔的有效腔长作为温度传感参量，可以避免可调谐激光光源的波长波动影响，将光纤光栅温度传感器测量精度提高到0.11 mK，达到国际先进水平。.③ 发表了一种基于移频锁定和随机激光的超高分辨率光纤应变测量技术，实现了140 fϵ∕√Hz @ 1 kHz的动态应变测量分辨率。.（2）解调算法方面.开展了光纤光栅反射谱降噪以及基于EMD-SG的高精度光纤光栅解调信号解调算法研究，将光纤光栅反射谱信噪比提高了10 dB，实现了低信噪比下0.68 nε的静态应变测量分辨率。.（3）应用研究方面.① 将高精度光纤光栅静态应变解调技术用于宽频带光纤地震仪的设计中，其自噪声水平为2.7 × 10-7 ms-2/√Hz@0.1 Hz，可以清晰地记录到数十公里的微震和数千公里以外的大震信号。.② 采用边带扫频激光技术实现了高精度多参量光纤光栅信号同步解调，研制出了光纤地壳形变、地震与温度多参量传感系统，系统应变与温度测量分辨率分别达到4.7 × 10-10、0.06 mK，能够同时记录到清晰的固体潮汐信号、地震波信号以及环境温度扰动。.上述研究成果，可为高精度的光纤地壳形变、地震传感装备研发提供核心技术支撑，进而为地壳板块驱动机制、断裂活动、地震发生过程等科学研究提供先进的技术手段。