Abstract
Optical Frequency Domain Reflectometry (OFDR) is used to make temperature distributed sensing measurements along a fiber by exploiting Rayleigh backscattering. This technique presents high spatial and high temperature resolutions on temperature ranges of several hundred of degrees Celsius. With standard telecommunications fibers, measurement errors coming from the correlation between a high temperature Rayleigh trace and the one taken as a reference at room temperature could be present at extremely high temperatures. These correlation errors, due to low backscattering signal amplitude and unstable backscattering signal, induce temperature measurement errors. Thus, for high temperature measurement ranges and at extremely high temperatures (e.g., at 800 °C), a known solution is to use fibers with femtosecond laser inscribed nanograting. These fs-laser-insolated fibers have a high amplitude and thermally stable scattering signal, and they exhibit lower correlation errors. In this article, temperature sensing at 800 °C is reported by using an annealed zirconia-doped optical fiber with an initial 40.5-dB enhanced scattering signal. The zirconia-doped fiber presents initially OFDR losses of 2.8 dB/m and low OFDR signal drift at 800 °C. The ZrO2-doped fiber is an alternative to nanograting-inscribed fiber to make OFDR distributed fiber sensing on several meters with gauge lengths of 1 cm at high temperatures.
Highlights
Optical fibers are used to make sensing measurements in severe environments, especially at high temperature, due to their different interesting properties: they are compact and insensitive to electromagnetic interference; several sensing techniques allow measurements at several positions along the same fiber [1]
The relaxation may allow slow and small physical changes of ZrO2 entities like crystallite size, crystal phase change, nucleation and crystallization of nanoparticles in glass matrix or chemical diffusion. These changes of zirconia entities characteristics would increase Rayleigh scattering in glass fiber’s core. This increase of Rayleigh scattering due to particles is high enough to counterbalance the decrease of Rayleigh scattering due to relaxation of silica glass, which should occur at the same time during test at high temperature (OFDR signal amplitude of SMF-28 fiber decreases by 1 dB during the same test at 800 ◦ C)
This paper presents a single-mode zirconia-doped fiber as a potential solution for temperature measurement by Optical Frequency Domain Reflectometry (OFDR) at 800 ◦ C and a 40 cm long section has been tested
Summary
Optical fibers are used to make sensing measurements in severe environments, especially at high temperature, due to their different interesting properties: they are compact and insensitive to electromagnetic interference; several sensing techniques allow measurements at several positions along the same fiber [1]. Several techniques exploit light backscattering (Brillouin, Raman or Rayleigh scatterings) to make distributed temperature sensing along the studied optical fiber. For OFDR temperature distributed sensing, tested optical fiber is used as a sensor and it is put along positions where temperature is to be measured. The second explanation is that physical and chemical changes in the fiber at high temperature modify permanently the Rayleigh scattering profile (these changes are confirmed by annealing tests on fibers at 900 ◦ C [9]), decreasing the similarity of a OFDR measurement compared to the reference one. After an annealing step to stabilize physical and chemical properties of ZrO2 -doped optical fiber, performances of tested ZrO2 -doped fiber are better than the ones of SMF-28 fiber This ZrO2 -doped fiber is a promising alternative to nanograting-inscribed fiber for stable distributed sensing applications at around 800 ◦ C
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