Toward a practical fiber-optic primary thermometer for industrial applications

We present our work toward the development of a fiber-optic primary thermometer based on refractive-index gas thermometry (RIGT) using argon as the working gas. The sensor is a Fabry-Pérot (FP) cavity at the tip of a single-mode optical fiber, with temperature determined from FP wavelength shifts at two pressure levels via a virial-coefficient model. Measurements from room temperature to ~1073 K agreed with a reference thermocouple within 1.0 K. Repeatability was ~±0.2K at ~300 K and increased to >±1.0°C near 1073 K. The compact, high-temperature-capable design offers a promising route to primary thermometry with potential for industrial deployment.