Chen Ming, Rao Xing, Liu Kuan, Wang Yuhang, Chen Shuqing, Xu Lin, Xu Rendong, Chen George Y, Wang Yiping
Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education/Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
Shenzhen Key Laboratory of Photonic Devices and Sensing Systems for Internet of Things, Guangdong and Hong Kong Joint Research Centre for Optical Fibre Sensors, State Key Laboratory of Radio Frequency Heterogeneous Integration, Shenzhen University, Shenzhen 518060, China.
Sensors (Basel). 2024 Aug 14;24(16):5257. doi: 10.3390/s24165257.
For distributed fiber-optic sensors, slowly varying vibration signals down to 5 mHz are difficult to measure due to low signal-to-noise ratios. We propose and demonstrate a forward transmission-based distributed sensing system, combined with a polarization-generated carrier for detection bandwidth reduction, and cross-correlation for vibration positioning. By applying a higher-frequency carrier signal using a fast polarization controller, the initial phase of the known carrier frequency is monitored and analyzed to demodulate the vibration signal. Only the polarization carrier needs to be analyzed, not the arbitrary-frequency signal, which can lead to hardware issues (reduced detection bandwidth and less noise). The difference in arrival time between the two detection ends obtained through cross-correlation can determine the vibration position. Our experimental results demonstrate a sensitivity of 0.63 mrad/με and a limit of detection (LoD) of 355.6 pε/Hz at 60 Hz. A lock-in amplifier can be used on the fixed carrier to achieve a minimal LoD. The sensing distance can reach 131.5 km and the positioning accuracy is 725 m (root-mean-square error) while the spatial resolution is 105 m. The tested vibration frequency range is between 0.005 Hz and 160 Hz. A low frequency of 5 mHz for forward transmission-based distributed sensing is highly attractive for seismic monitoring applications.
对于分布式光纤传感器，由于信噪比低，低至5毫赫兹的缓慢变化振动信号很难测量。我们提出并演示了一种基于正向传输的分布式传感系统，该系统结合了用于降低检测带宽的偏振产生载波和用于振动定位的互相关。通过使用快速偏振控制器施加更高频率的载波信号，监测并分析已知载波频率的初始相位来解调振动信号。只需要分析偏振载波，而不是任意频率信号，因为任意频率信号可能会导致硬件问题（降低检测带宽和增加噪声）。通过互相关获得的两个检测端之间的到达时间差异可以确定振动位置。我们的实验结果表明，在60赫兹时灵敏度为0.63毫弧度/微应变，检测限（LoD）为355.6皮应变/赫兹。可以在固定载波上使用锁相放大器以实现最小检测限。传感距离可达131.5公里，定位精度为725米（均方根误差），而空间分辨率为105米。测试的振动频率范围在0.005赫兹至160赫兹之间。对于基于正向传输的分布式传感，5毫赫兹的低频对于地震监测应用极具吸引力。
