Takada Kazumasa, Satoh Shin-Ichi, Kawakami Akiya
Division of Electronics and Informatics, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan.
Sensors (Basel). 2020 Feb 10;20(3):936. doi: 10.3390/s20030936.
Signal-dependent speckle-like noise was the dominant noise in a Brillouin grating measurement with micrometer-resolution optical low coherence reflectometry (OLCR). The noise was produced by the interaction of a Stokes signal with beat noise caused by a leaked pump light via square-law detection. The resultant signal-to-noise ratio (SNR) was calculated and found to be proportional to the square root of the dynamic range (DR) defined by the ratio of the Stokes signal magnitude to the variance of the beat noise. The calculation showed that even when we achieved a DR of 20 dB on a logarithmic scale, the SNR value was only 7 on a linear scale and the detected signal tended to fluctuate over ±14% with respect to the mean level. We achieved an SNR of 24 by attenuating the pump light power entering the balanced mixer by 55 dB, and this success enabled us to measure the Brillouin spectrum distributions of mated fiber connectors and a 3-dB fused fiber coupler with a micrometer resolution as examples of OLCR diagnosis.
在采用微米级分辨率光学低相干反射仪（OLCR）进行的布里渊光栅测量中，与信号相关的散斑状噪声是主要噪声。该噪声是由斯托克斯信号与通过平方律检测的泄漏泵浦光引起的拍频噪声相互作用产生的。计算了所得的信噪比（SNR），发现其与由斯托克斯信号幅度与拍频噪声方差之比定义的动态范围（DR）的平方根成正比。计算表明，即使在对数尺度上实现了20 dB的动态范围，在线性尺度上SNR值也仅为7，并且检测到的信号相对于平均水平倾向于在±14%范围内波动。通过将进入平衡混频器的泵浦光功率衰减55 dB，我们实现了24的SNR，这一成功使我们能够以微米级分辨率测量配对光纤连接器和3 dB熔接光纤耦合器的布里渊光谱分布，作为OLCR诊断的示例。
