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A novel BOTDA method based on differential π-phase-shift-pulse pair is proposed for narrowing the Brillouin gain spectrum. Theoretical analysis and experimental results demonstrate that the proposal could achieve 17 MHz Brillouin gain spectrum linewidth with a fixed spatial resolution of 2.5 m. The Brillouin gain spectrum linewidth is 3 times narrower than that obtained using conventional single-pulse...
The frequency division multiplexing (FDM) technique is firstly introduced into a direct-detection phase-sensitive OTDR to improve the distributed fiber acoustic sensing performance by using a frequency step sweeping laser source and a dual probe pulse scheme. By using FDM technique, a 40 kHz sampling rate to vibration is realized with a 10 km measurement range, which implies the tradeoff between the...
Temperature and strain discrimination is experimentally demonstrated in an elliptical-core polarization-maintaining fiber by making use of Rayleigh-based distributed birefringence measurements and the frequency shift of the correlation peak obtained by standard coherent optical time-domain reflectometry. The high sensitivity of coherent Rayleigh sensing and the very distinct behavior of birefringence...
We propose and demonstrate the use of cross recurrence plot analysis (CRPA) to accurately determine the Brillouin shift due to strain and temperature in a Brillouin distributed fiber sensor. This signal processing technique, which is implemented in Brillouin sensors for the first time relies on apriori data i.e, the lineshape of the Brillouin gain spectrum and its similarity with the spectral features...
Rotational Seismology caused highly interest in investigation of rotational movements generated by earthquake, mines and existing in engineering structures. The most oppressive aspect of research in this field is technical requirements for sensors. However, the instruments basing on the Sagnac effect seem to be the most appropriate to investigate rotational effects due to the fact that they are entirely...
High spatial resolution measurement of the Brillouin frequency shift (BFS) is accomplished using transient analysis. The step response of the output signal wave is recorded for an arbitrary, known frequency offset between pump and signal, and compared against a library of modeled, reference functions. No spectral scanning or prior knowledge of the BFS is necessary. The principle is employed in a Brillouin...
In this work, a fiber identification method based on incoherent optical frequency domain reflectometry (lOFDR) measurements is introduced. The proposed method uses the characteristic interference pattern of IOFDR Rayleigh backscatter measurements with a broadband light source to unambiguously recognize different initially scanned fiber segments. The recognition is achieved by crosscorrelating the...
We propose a model-based compressed sensing (MBCS) of FBG arrays (FBGA), interrogated with wavelength scanning incoherent optical frequency domain reflectometry. This method measures the frequency response of a FBGA with an electrical vector network analyzer combined with a tunable laser. Instead of the usual inverse discrete Fourier transform (IDFT), we apply a direct estimation of the grating reflectivities...
We review our recent work on chirped-pulse phase-sensitive optical time-domain reflectometry along optical fibers and its application in the measurement of true nanostrain variations in the kHz frequency range over km-long fibers. We also show how this technique can be used to perform distributed photothermal measurements of gas presence in suitable microstructured fibers.
Brillouin distributed optical fiber strain sensors are often limited to static events because of the long acquisition time due to the classic frequency sweep technique. Recently, BOTDA sensor based on slope-assisted (SA) method has been proposed for fast strain measurement along the sensing fiber. In this paper, we present a novel dynamic SA-BOTDR for single-ended truly distributed strain measurement...
The measurement accuracy of dynamic fiber-optic sensing interrogators, which use frequency scanning to determine the value of the measurand, err as either the event bandwidth approaches half the instrument sampling frequency or when the event dynamic range comes close to the instrument designed value. One main source of error is the common practice of assigning sampling at a non-uniform grid to a...
A frequency-domain method is proposed to measure the inertial response of forward stimulated Brillouin scattering, so that the acoustic impedance of a liquid medium outside an uncoated 30 m standard single-mode fibre can be sensed. The proposed technique overcomes the linewidth distortion present in the time-domain approach due to Kerr effect and reduce time and complexity for data post-processing...
A new scheme for fast distributed sensing based on Brillouin Optical Time-Domain Analysis (BOTDA) is proposed and demonstrated, based on the use of a frequency swept microwave source for the generation of the probe wave. The entire BOTDA measurement is taken within the duration of the frequency sweep, at a frequency granularity depending on the duration of the sweep, the repetition rate of the pump...
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