Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov Street 38, 119991 Moscow, Russia.
Petrofiber, LLC, Klinsky Proezd 7, 301664 Novomoskovsk, Russia.
Sensors (Basel). 2023 Jun 7;23(12):5402. doi: 10.3390/s23125402.
In the paper, the effect of spontaneous Brillouin scattering (SpBS) is analyzed as a noise source in distributed acoustic sensors (DAS). The intensity of the SpBS wave fluctuates over time, and these fluctuations increase the noise power in DAS. Based on experimental data, the probability density function (PDF) of the spectrally selected SpBS Stokes wave intensity is negative exponential, which corresponds to the known theoretical conception. Based on this statement, an estimation of the average noise power induced by the SpBS wave is given. This noise power equals the square of the average power of the SpBS Stokes wave, which in turn is approximately 18 dB lower than the Rayleigh backscattering power. The noise composition in DAS is determined for two configurations, the first for the initial backscattering spectrum and the second for the spectrum in which the SpBS Stokes and anti-Stokes waves are rejected. It is established that in the analyzed particular case, the SpBS noise power is dominant and exceeds the powers of the thermal, shot, and phase noises in DAS. Accordingly, by rejecting the SpBS waves at the photodetector input, it is possible to reduce the noise power in DAS. In our case, this rejection is carried out by an asymmetric Mach-Zehnder interferometer (MZI). The rejection of the SpBS wave is most relevant for broadband photodetectors, which are associated with the use of short probing pulses to achieve short gauge lengths in DAS.
在本文中，分析了自发布里渊散射（SpBS）作为分布式声学传感器（DAS）中的噪声源的影响。SpBS 波的强度随时间波动，这些波动会增加 DAS 中的噪声功率。基于实验数据，光谱选择的 SpBS 斯托克斯波强度的概率密度函数（PDF）呈负指数分布，这与已知的理论概念相对应。基于这一说法，给出了 SpBS 波引起的平均噪声功率的估计。该噪声功率等于 SpBS 斯托克斯波的平均功率的平方，而该平均功率又比瑞利后向散射功率低约 18dB。确定了 DAS 中的噪声组成，第一种情况是初始后向散射谱，第二种情况是 SpBS 斯托克斯波和反斯托克斯波被拒绝的谱。结果表明，在所分析的特定情况下，SpBS 噪声功率占主导地位，超过了 DAS 中的热噪声、散粒噪声和相位噪声的功率。因此，通过在光电探测器输入端拒绝 SpBS 波，可以降低 DAS 中的噪声功率。在我们的情况下，这种拒绝是通过非对称马赫-曾德尔干涉仪（MZI）实现的。对于宽带光电探测器来说，SpBS 波的拒绝是最相关的，因为宽带光电探测器与使用短探测脉冲来实现 DAS 中的短测量长度有关。
