Abstract
Brillouin-based fiber-optic sensing has been regarded as a powerful distributed measurement tool for monitoring the conditions of modern large civil and geotechnical structures, since it provides continuous environmental information (e.g., temperature and strain) along the whole fiber used for sensing applications. In the past few decades, great research efforts were devoted to improve its performance in terms of measurement range, spatial resolution, measurement speed, sensitivity, and cost-effectiveness, of which the slope-assisted measurement scheme, achieved by exploiting the linear slope of the Brillouin gain spectrum (BGS), have paved the way for dynamic distributed fiber-optic sensing. In this article, slope-assisted Brillouin-based distributed fiber-optic sensing techniques demonstrated in the past few years will be reviewed, including the slope-assisted Brillouin optical time-domain analysis/reflectometry (SA-BOTDA/SA-BOTDR), the slope-assisted Brillouin dynamic grating (BDG) sensor, and the slope-assisted Brillouin optical correlation domain analysis/reflectometry (SA-BOCDA/SA-BOCDR). Avenues for future research and development of slope-assisted Brillouin-based fiber-optic sensors are also prospected.
Highlights
Aging degradation and seismic damage of civil infrastructures such as bridges, pipelines, and buildings have posed a serious issue for public security
[14, 15]; spatial resolution is of the order of a few millimeters [16,17,18,19]; dynamic events can be captured at sampling rates as Advanced Devices & Instrumentation high as MHz [20, 21]; temperature/strain sensitivity has been enhanced by a factor of six by exploiting the high-order Stokes waves [22, 23]
Where PðzÞ is the pump power at z, g0 is the Brillouin gain coefficient, ν is the frequency interval between the pump wave and probe wave, νBðzÞ is the Brillouin frequency shift (BFS) at location z, whose typical value is 11 GHz for single-mode fibers (SMFs), ΔνB is the full width as half maximum (FWHM) of the Brillouin gain spectrum (BGS), whose typical value is 35 MHz, and K is a coefficient determined by material constants and the relative polarizations of the pump wave and Stoke wave
Summary
Aging degradation and seismic damage of civil infrastructures such as bridges, pipelines, and buildings have posed a serious issue for public security. In a Brillouin-based sensing system, the whole Brillouin gain spectrum (BGS) is supposed to be measured by sweeping the frequency interval between the pump wave and Stoke wave, to extract the BFS and to obtain the temperature/strain information along the FUT. A novel measurement scheme called slope-assisted technique has been proposed by exploiting the linear slope of the BGS [24] In this scheme, the frequency interval between the pump wave and probe (or reference) wave is fixed at the middle of the BGS linear slope, to convert the temperature/ strain-induced BFS change to Brillouin signal power variation, where the frequency sweeping process is avoided and the sampling rate is improved significantly.
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