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.
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.
We demonstrate a narrow-linewidth laser source for high spatial resolution distributed optical sensing by utilizing the high-order modulation sidebands injection locking. A pair of phase-locked lasers with arbitrary frequency offset from 5 GHz to 50 GHz is generated. Meanwhile, a linearized frequency sweep covering range of 15 GHz in 6 ms with frequency errors of 240 kHz from linearity is also achieved using the same scheme, the instantaneous linewidth of the frequency-swept laser is measured to be ~2.5 kHz.