Abstract
Under extreme conditions such as cryogenic temperatures, the application of optical fiber sensors inevitably encounters significant challenges, which include the calibrations associated with the thermal problems of sensor placement and heat sinking and the nonlinear dependence of cryogenic temperatures. Thus, fundamental investigations involving high-precision calibrations of the strain and temperature at cryogenic temperatures are essential. To this end, in this study, the thermo-optic coefficient, temperature and strain sensitivity coefficients for a Rayleigh-scattering-based distributed optical fiber sensor (DOFS) were calibrated. This experiment was implemented using a self-built low-temperature test device, and the calibration study was conducted over a large cryogenic temperature range, from 77 K to room temperature. The results indicated that the strain sensitivity coefficient of the Rayleigh-scattering-based DOFS is temperature-independent, whereas the temperature sensitivity coefficient has a significantly nonlinear temperature dependence and is associated with the coating polymer layers of the fiber. The coefficients and fitting functions were obtained over a large range of cryogenic temperatures, which indicated the invaluable properties of optical fibers in practice. Furthermore, the strain and temperature of an aluminum beam under thermal and bending loads were measured. The results indicated good agreement between the optical fibers and strain gauges, which verified the availability and reliability of Rayleigh-scattering-based distributed optical fibers in cryogenic environments.
Published Version
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