Design and research of a dual-hole reflective optical fiber temperature sensor

• A dual-hole reflective fiber optic temperature sensor is designed for real-time liquid temperature detection in strong magnetic fields/small spaces, utilizing liquid refractive index-temperature dependence without traditional thermosensitive materials. • Compared with single-hole probes, the dual-hole structure reduces bubble interference, enhances heat exchange, achieving 6.8% linearity (vs 9.2%) and 0.76mV/°C sensitivity (vs 0.75mV/°C) with better stability. • A mathematical model based on Gaussian-like optical field distribution is established, analyzing effects of reflection distance, axial spacing, NA, and core radius on sensitivity for optimization. • Static calibration confirms both probes work at 30-122°C; dual-hole shows higher linear fitting degree, smaller errors, suitable for oil temperature monitoring in strong magnetoelectric environments. Aiming at the real-time detection of liquid temperature in special environment such as strong magnetic field and small space, a double-hole reflective fiber optic temperature sensor was designed based on the law of liquid refractive index with temperature and the propagation characteristics of light in liquid. On the basis of proposing the principle of temperature measurement using reflective fiber optic temperature sensors, the probe structure of the sensor was determined. A mathematical model of the sensor was established based on the approximate Gaussian distribution of the optical field at the fiber end, and the influence of different parameters on the output characteristics of the sensor was analyzed. Building an experimental platform and conducting respectively static calibration experiments on fiber optic sensors with single hole and double hole inlet probe structures. The results showed that both types of inlet sleeve structure sensors can achieve liquid detection in the temperature range of 30–122 °C. The sensitivity of the single hole probe reflective fiber optic sensor is 0.75 mV/°C, with a linearity of 9.2 %; The linearity of the dual hole reflective fiber optic sensor is 6.8 %, and the sensitivity is 0.76 mV/°C. The dual hole structure has lower linearity and higher fit degree during linear fitting.