Enhanced cryogenic measurement: Rayleigh-Scattering measurements with dual optical fibers for precise decoupling of temperature and strain

Assessing the operational dynamics of high-temperature superconducting coils during cooling and excitation is essential for their reliable performance and longevity. Rayleigh-scattering-based optical frequency-domain reflectometry distributed optical-fiber sensors (DOFSs) offer a promising solution to real-time monitoring in extreme conditions such as in the presence of intense electromagnetic fields and at cryogenic temperatures; these devices boast immunity to electromagnetic interference and high spatial resolution, and they can be embedded in superconducting coils without compromising their integrity. However, they typically face difficulties distinguishing between thermal and mechanical strains in environments above the temperature of liquid nitrogen. To counter this, we embedded a pair of single-mode Rayleigh-scattering DOFSs side by side-one encased in miniscule capillary tubing to exclusively measure temperature, and the other to measure both strain and temperature. Across a wide temperature range from 77 K to room temperature, we systematically calibrated the temperature- and strain-sensitivity coefficients and demonstrated the technique's accuracy through comparison against conventional sensors by applying nonuniform tensile and thermal stresses. This dual-sensor approach provides a robust and non-disruptive strategy for the precise measurement of distributed temperature and strain in cryogenic environments.