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Temperature-Strain Discrimination Using the Brillouin Frequency and Linewidth
[Technical Report, Memorandum Report]
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
Distributed fiber optic sensors that can measure and discriminate between temperature and strain have many important applications including 3-dimensional shape sensing and structural health monitoring. A Brillouin-based sensor is a promising choice for these applications since the Brillouin frequency and the Brillouin linewidth have different dependencies on the temperature and strain in the fiber. Here, we designed and constructed a Brillouin optical time-domain analysis BOTDA system for this purpose using an optical frequency comb. The system extracts the Brillouin frequency and linewidth at each position in the fiber from the measured Brillouin gain spectrum. The temperature and strain can then be recovered at each position along the fiber under test. We show that this approach enables a temperature resolution of 2 oC and a strain resolution of 50 with a 10 m sensing aperture. Finally, we discuss the limitations of this technique due to non-uniformities within the sensing aperture and provide a comparison with alternative schemes for temperaturestrain discrimination.
[A, Approved For Public Release]