Simultaneous distributed measurement of strain and temperature from noise-initiated Brillouin scattering in optical fibers

Distributed Temperature Sensing: Review of Technology and Applications

“…The Brillouin scattering produces both frequency down-(Stokes) and up-shifted (AntiStokes) light, given by (1) where, is the Brillouin frequency shift, is the angular frequency shift, is the refractive index of the fiber, is the longitudinal acoustic velocity for the fiber, and is the free-space wavelength of the pump light [7]. The Brillouin frequency shift varies linearly with the strain and the temperature, as given by [7] (2) For m, the strain and the temperature coefficients of the Brillouin frequency shift, due to the strain and the temperature , are measured as ( m) and ( MHz/K), respectively [8]. Thus, the Brillouin scattering-based technique can be used for sensing both distributed temperature and strain, but not simultaneously both.…”

“…The different coefficients would be utilized to separate the effects, provided one is interested to measure either the temperature or the strain, but not in a mixed-mode. Even though Parker et al [7] studied possible ways to simultaneously detect temperature and strain using the Brillouin scattering, that is not quite standard yet.…”

Applications of In–Fiber Acousto–Optic Devices

“…The central (highest) peak corresponds to the proper laser beam reflections after successive connections and splices together with Rayleigh scattering. Peaks symmetrically positioned at both sides correspond to the Brillouin backscattering by Stokes and anti-Stokes processes (Parker et al, 1998). The measured Brillouin shift results in 88 pm (i.e.…”

“…Fiber optics distributed temperature, and/or strain, sensors have becoming very attractive for applications requiring sensing lengths of many kilometers, principally due to its inexpensiveness and availability. Optical fiber based distributed sensor systems normally make use of the principle of optical time domain reflectometry (Parker et al, 1998). Therefore, an optical pulse is launched into one end of the fiber system and the variation of the scattered light is detected as a function of time, giving in this way information of temperature or strain as a function of distance.…”

“…When a coherent pulse of light propagates through a medium, part of its energy is backscattered due to a non elastic interaction with the acoustic phonons. This back-scattered light is composed of a frequency down-shifted Stokes light and an up-shifted anti-Stokes light, whose spectral positions are dependent on temperature and strain of the fiber, in this way allowing its use as a sensing mechanism (Culverhouse et al, 1989a(Culverhouse et al, , 1989bBao et al, 1995;Parker et al, 1998;Y. Li et al, 2003).…”