31 January 2012 The non-uniformity and dispersion in SBS-based fiber sensors
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Proceedings Volume 8351, Third Asia Pacific Optical Sensors Conference; 83512Y (2012); doi: 10.1117/12.916230
Event: Asia Pacific Optical Sensors Conference, 2012, Sydney, Australia
Abstract
For a fiber with complex index profile, its density fluctuations change with position and it also introduces birefringence, hence the Brillouin frequency changes with position due to variation of modal index, and sound velocity has a range instead of being a constant. As a result, the single mode fibers support multiple Brillouin resonances varying in position, even with polarization scramblers (PS) of the pump and probe waves. For a Brillouin optical time domain analysis (BOTDA), at a specific location, because of the spatial resolution, the measured Brillouin frequency still gives a range, although PS can help to reduce this fluctuation, as the spatial resolution is much smaller than the beat length of single mode fiber (SMF). The measured Brillouin frequency variations in one position and its location dependence reflect the non-uniformity of the optical fiber, rather than the systematic error of the sensor detection system. When a fiber supports elliptical birefringence, then four Brillouin resonances can be found for an acoustically uniform fiber based on theoretical calculation of their eigenmodes. The beat of different Brillouin peak frequencies and their magnitudes change with temperature and strain, which can be used to measure temperature and strain simultaneously in LEAF fiber without the need of the sweeping Brillouin spectrum.
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Xiaoyi Bao, Shangran Xie, Xuan Liu, Liang Chen, "The non-uniformity and dispersion in SBS-based fiber sensors", Proc. SPIE 8351, Third Asia Pacific Optical Sensors Conference, 83512Y (31 January 2012); doi: 10.1117/12.916230; https://doi.org/10.1117/12.916230
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KEYWORDS
Acoustics

Birefringence

Polarization

Optical fibers

Temperature metrology

Refractive index

Scattering

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