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Distributed time delay sensing in a random fiber grating array based on chirped pulse phi-OTDR

机译：基于啁啾脉冲PHI-OTDR的随机光纤光栅阵列中的分布式时间延迟感测

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摘要

A high-precision distributed time delay measurement in a chirped pulse phase optical time domain reflectometry (CP phi-OTDR) system based on a random fiber grating array is proposed and demonstrated, in which a temperature-induced refractive index and fiber dimension change associated time delay could be measured for distributed temperature sensing. The random fiber grating array includes many inscribed refractive index change locations at periods of sub-micron. When laser pulses are launched into the fiber grating, the backscattered light possesses many unique localized speckle patterns at different locations. These patterns change with temperature, and hence the backscattering spectral response will change accordingly. By measuring the localized speckle pattern change due to the change of the temperature over the chirped pulse spectrum and performing cross-correlation calculation, we can realize distributed temperature measurements in real time using a megahertz bandwidth distributed feedback laser. Unlike a conventional phi-OTDR sensing system which measures a distributed phase change along the fiber using an ultra-narrow linewidth laser, the distributed time delay presented in this Letter is directly measured in real time. It is shown that the time-resolved localized pattern trace is stable with very small fluctuation, thanks to the enhanced inhomogeneity and reflectivity. The minimum detectable temperature variation is about 0.028 degrees C at meter order of magnitude spatial resolution. (C) 2020 Optical Society of America
机译：在啁啾脉冲相位光时域反射高精度的分布的时间延迟测量（CP PHI-OTDR）基于随机光纤光栅阵列系统提出并展示，其中，温度引起的折射率和纤维尺寸变化相关联的时间延迟可以为分布式温度感测来测量。随机光纤光栅阵列包括在亚微米的周期许多内接的折射率变化的位置。当激光脉冲发射到光纤光栅，反向散射光具有在不同位置的许多独特的局部散斑图案。这些模式随温度变化，并且因此背散射光谱响应将相应地改变。通过测量由于温度在啁啾脉冲的频谱和进行互相关计算的变化的局部散斑图案的变化，就可以实现使用兆赫带宽分布反馈激光器在实时分布式温度测量。不同于传统的PHI-OTDR感测系统，其测量沿使用超窄线宽激光光纤分布式相位变化，在此提出的信分布的时间延迟被实时直接测量。结果表明，时间分辨本地化的模式跟踪稳定具有非常小的波动，这要归功于增强的不均匀性和反射率。最小可检测的温度变化是约在米数量级的空间分辨率的0.028摄氏度。 （c）2020美国光学学会

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