Abstract
Using a novel range-resolved interferometric signal processing
technique based on the sinusoidal optical frequency modulation of a
cost-effective laser diode, a fiber sensing approach termed fiber segment
interferometry (FSI) is described. In FSI, a chain of long-gauge length
fiber optic strain sensors are separated by identical in-fiber partial
reflectors. Targeted at dynamic strain analysis and ultrasound detection
for structural health monitoring, this approach allows integrated strain
measurements along fiber segments, removing the sensing gaps and
sensitivity to inhomogeneities found with localized fiber sensors. In this
paper, the multiplexing of six fiber segments, each of length 12.5 cm, is
demonstrated. The sensor array can be interrogated at 98 kHz data rate,
achieving dynamic strain noise levels
$\leq 0.14\,\mathrm{n\epsilon \cdot Hz^{-0.5}}$
. The reflector fabrication is discussed, an analysis of
linearity and noise performance is carried out and results from an
exemplar experiment to determine the speed-of-sound of a stainless steel
rod are shown.
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