研究目的
To demonstrate a technology for position-resolved measurement of nanostrain perturbations along optical fibers for use as a dense and ultrasensitive seismic sensor array, with applications in seismology and other fields.
研究成果
The CP-ΦOTDR technology is a highly sensitive and dynamic tool for distributed sensing, capable of meter-scale resolution over long distances. It shows promise for applications in seismology, chemical sensing, and wind speed measurement, with potential for integration into existing fiber networks for earthquake early warning systems and other monitoring purposes.
研究不足
Challenges include tracking slow variations over months while registering high-frequency signals, laser phase noise that requires subtraction, and range limitations due to optical loss, though mitigated by Raman amplification. The technology may face issues in very long-range deployments without amplification.
1：Experimental Design and Method Selection:
The method is based on chirped-pulse phase-sensitive optical time domain reflectometry (CP-ΦOTDR), which uses linearly-chirped probe pulses to achieve linear mapping of perturbations. It involves detecting and digitizing optical echoes and computing correlations of consecutive traces to measure local time shifts proportional to temperature or strain changes.
2：Sample Selection and Data Sources:
The fiber under test (FUT) is a conventional optical fiber cable, with specific setups for different applications (e.g., holey optical fiber for chemical sensing, metal-coated fiber for wind speed measurement).
3：List of Experimental Equipment and Materials:
Equipment includes a continuous wave laser source (LD), semiconductor optical amplifier (SOA), erbium-doped fiber amplifier (EDFA), band-pass filter, fast p-i-n photodetector, electronics for digitization, and a computer for processing. Materials include optical fibers and coatings as specified.
4：Experimental Procedures and Operational Workflow:
Pulses are generated by modulating the LD bias current, amplified and filtered, sent into the FUT, and backscattered light is amplified, filtered, detected, digitized, and processed in real-time using GPU-based computing.
5：Data Analysis Methods:
Data analysis involves computing correlations of consecutive power traces to determine local time shifts, converting these to temperature or strain variations using theoretical coefficients, and applying denoising techniques for laser phase noise removal.
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