Chirped Fiber Brillouin Frequency-Domain Distributed Sensing
Journal Article - Open Access
University of Illinois - Urbana Champaign United States
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A frequency-domain distributed temperaturestrain sensor based on a longitudinally graded optical fiber LGF is proposed and evaluated. In an LGF, the Brillouin scattering frequency, subB , changes i.e., is chirped lengthwise monotonically and thus every position along the fiber has a unique subB . Any change locally at some position in the fiber environment will result in a measurable change in the shape of the Brillouin gain spectrum BGS near the frequency component mapped to that position. This is demonstrated via measurements and modeling for an LGF with local heating. The LGF is one with 100MHz Brillouin frequency gradient over 16.7 m, with 1.1 and 1.7 m segments heated up to 40 K above ambient. A measurement of the BGS can enable the determination of a thermal or strain distribution along a sensor fiber, thus rendering the system one that is in the frequency domain. A sensitivity analysis is also presented for both coherent and pump-probe BGS measurement schemes. The modeling results suggest that the frequency-domain systems based on fibers with a chirped Brillouin frequency are highly suited as inexpensive event sensors alarms and have the potential to reach submeter position determination with sub-1-K temperature accuracies at 1kHz sampling rates. Limitations to the technique are discussed.
- Fiber Optics and Integrated Optics
- Optical Detection and Detectors