相位敏感光时域反射系统低频响应性能优化

相位敏感光时域反射系统以其分布式光纤传感技术的优势在分布式水听、压裂微地震检测、自然灾害预警等低频监测领域具有极高的应用前景。文中对系统中脉冲斩波信号与频率调制信号时钟不同源的问题予以验证，并对其产生的影响进行理论分析；设计双路同步时钟源驱动产生脉冲斩波信号和频率调制信号，降低每个脉冲重复周期中频率调制信号的随机低频相位噪声，提高探测脉冲光的相位稳定性；采用时钟同源和时钟非同源两种方式对典型的基于外差相干检测的相位敏感光时域反射系统的声光调制器进行驱动，由信号发生器驱动缠有光纤的压电陶瓷，产生不同频段的扰动信号。实验结果表明:在同一测试条件下，前者在低频段的信噪比、相位解调质量、频率响应方面均优于后者，最小响应频率为0.1 Hz，相对提高两个数量级，降低了系统中低频噪声干扰。该方法易于实现，可与现有的低频性能优化方法或结构兼容，进一步提高系统低频响应性能。

Optimization of low frequency response performance of phase sensitive optical time-domain reflectometry system

Phase sensitive optical time-domain reflectometry system due to its advantages of distributed optical fiber sensing technology has a high application prospect in low frequency monitoring fields such as distributed hydrophone, fracture micro-seismic detection and natural disaster warning. The problem of different clock source of pulse chopper signal and frequency modulated signal in the system was verified and the influence was analyzed theoretically in this paper. A dual-channel synchronous clock source was designed to generate pulse chopper signal and frequency modulation signal to reduce the random low-frequency phase noise of frequency modulation signal in each pulse repetition period and improve the phase stability of the detection pulse light. The acousti-optic modulator of typical phase-sensitive optical time-domain reflectometry system based on heterodyne coherent detection was driven by clock homology and clock non-homology, a signal generator drives a piezoelectric ceramic wrapped in optical fibers to generate disturbance signals in different frequency bands. The experimental results show that under the same test conditions, the former is superior to the latter in the aspects of SNR, phase demodulation quality and frequency response in low frequency band. The minimum response frequency is 0.1 Hz, which is 2 orders of magnitude higher than the latter, and reduces the interference of low frequency noise in the system. The method was easy to implement and compatible with the existing low frequency performance optimization methods or structures to further improve the low frequency response performance of the system.