布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.

Principle of Brillouin dynamic grating and its applications in optical fiber sensing

Brillouin dynamic grating (BDG) has been widely studied since it was proposed for the first time to achieve optical storage in 2007. In general, when two beams of pump light (their frequency difference equal to Brillouin frequency shift of the optical fiber) with the same polarization state are injected into the fiber, the coherent acoustic wave can be excited by the stimulated Brillouin scattering effect, forming a BDG. The BDG in an optical fiber has been widely used in optical fiber sensing, characterization of optical fibers, optical storage, all-optical signal processing, microwave photonics and high-precision spectral analysis due to the advantages of all-optical generation and flexible parameter control. In this paper, we analyze the principle of BDG generation and detection, and its applications in optical fiber sensing. The simultaneous measuring of strain and temperature is achieved within a spatial resolution of 20 cm through measuring Brillouin frequency shift and birefringence-induced frequency shift in a polarization-maintaining fiber. A high-sensitivity distributed transverse load sensor based on BDG with a measurement accuracy as high as 0.8×10^-3 N/mm is proposed and demonstrated, whose principle is to measure the transverse-load-induced birefringence change through exciting and probing a BDG in an elliptical-core polarization maintaining fiber. On the basis of the above research, a distributed measurement of hydrostatic pressure is demonstrated by using a 4-m photonics crystal fiber with a measurement error less than 0.03 MPa at a 20-cm spatial resolution, while the temperature cross-talk to the hydrostatic pressure sensing can be compensated for through measuring the temperature-induced Brillouin frequency shift changes by using Brillouin optical time-domain analysis. A system based on BDG in polarization maintaining fibers is reported to achieve a spatial resolution below one centimeter, while preserving the full accuracy on the determination of temperature and strain through measuring Brillouin frequency shift. Taking advantage of creating a long BDG in an optical fiber, an ultra-narrow bandwidth optical filter is realized by operating a BDG in a single-mode fiber, and the optical spectrometry is performed by sweeping the center wavelength of the BDG-based filter through a swept-tuned laser, where a 4 fm (0.5 MHz) spectral resolution is achieved by operating a BDG in a 400 m single-mode fiber.