High-speed railway is being developed rapidly; its safety, including infrastructure and train operation, is vital. This paper presents a railway-subgrade vibration monitoring scheme based on phase-sensitive OTDR for railway safety. The subgrade vibration is detected and rebuilt. Multi-dimension comprehensive analysis (MDCA) is proposed to identify the running train signals and illegal constructions along railway. To our best knowledge, it is the first time that a railway-subgrade vibration monitoring scheme is proposed. This scheme is proved effective by field tests for real-time train tracking and activities monitoring along railway. It provides a new passive distributed way for all-weather railway-subgrade vibration monitoring.
Proc. SPIE. 10323, 25th International Conference on Optical Fiber Sensors
KEYWORDS: Signal to noise ratio, Ferroelectric materials, Digital signal processing, Modulation, Data acquisition, Reflectometry, Frequency modulation, Spatial resolution, Bragg cells, Signal detection
We propose and experimentally demonstrate a pulse compression phase sensitive optical time domain reflectometer (φ- OTDR) with sub-meter resolution. Principle and theoretical analysis on the spatial resolution, the feasibility to obtain the phase information are provided. This technique can break the tradeoff between spatial resolution and measurement range in the traditional φ-OTDR. As example, our verifying experiment achieves 30cm spatial resolution and 20km measurement range, and the signal to noise ratio (SNR) reaches 10dB. To our knowledge, this is the first time that such a high spatial resolution over such a long sensing range is reported in φ-OTDR-based distributed vibration sensing.
Polarization fading is a phenomenon observed often in BOTDR distributed sensors, which greatly reduces signal-to-noise ratio of the detected signal. We proposed a scheme based on injecting optical pulse probes with orthogonal polarization states, which is generated by a delay Mach-Zehnder interferometer (MZI) composed of two polarization beam splitters (PBS). The principle is analyzed and the effect of reducing polarization fading is demonstrated experimentally. The method uses simple and passive components and is suitable for practical applications.