研究目的
To improve the spatial resolution of BOTDR sensors for distributed strain measurement using a differential cross spectrum technique based on intensity modulation.
研究成果
The proposed differential cross spectrum technique using intensity modulation successfully achieves high spatial resolution (0.2 m) and accurate BFS measurement (3.2 MHz) in BOTDR sensors, demonstrating effectiveness and ease of implementation compared to phase modulation methods.
研究不足
The technique may have limitations in longer fiber lengths or more complex fiber configurations, and the intensity modulation scheme could be optimized for better performance in various environmental conditions.
1：Experimental Design and Method Selection:
The experiment uses a differential cross spectrum technique in BOTDR, involving intensity modulation to generate a pair of pulsed probes (one with long and short pulses separated by an interval, and another with only the long pulse). FFT is applied to cross-correlations of backscattered signals sampled by wide and narrow window functions to achieve narrow Brillouin spectrum width and high spatial resolution.
2：Sample Selection and Data Sources:
A test fiber composed of single-mode fibers (SMF-1 and SMF-2) with a total length of about 350 m is used, with specific sections to evaluate spatial resolution and Brillouin frequency shift (BFS) accuracy.
3：List of Experimental Equipment and Materials:
Laser operating at 1550 nm, frequency shift modulator, amplitude keying modulator, optical amplifier, balanced photodetector (BPD), oscilloscope, single-mode fibers (SMF-1 and SMF-2).
4：2). Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Light from the laser is frequency-upshifted and amplitude-modulated to create pulsed probes, amplified to 300 mW, and injected into the fiber. Backscattered Brillouin signals interfere with local light and are detected by a BPD. The signal is sampled 56000 times by an oscilloscope and processed using FFT-based cross-correlation and differential calculations.
5：Data Analysis Methods:
Data is analyzed using FFT to compute cross-spectra, with BFS accuracy evaluated by standard deviation and spatial resolution confirmed by falling edge length at fiber boundaries.
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laser
Generates light at 1550 nm for the optical probe.
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frequency shift modulator
Upshifts the frequency of the laser light.
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amplitude keying modulator
Modulates the amplitude to generate pulsed probes.
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optical amplifier
Amplifies the optical probe to about 300 mW.
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balanced photodetector
BPD
Detects the interference signal between backscattered Brillouin signal and local light.
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oscilloscope
Samples the detected signal 56000 times for data processing.
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single mode fiber
SMF-1, SMF-2
Used as the test fiber for strain measurement, with different BFS characteristics.
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